I live in City of Ontario. Its right on the edge of the transition from inland valley to low desert. Im 25 miles from the beach, the mountains and the deserts of Palm Springs, so the climate here is usually the most annoying of any of those three. Its hot and dry during the summer, cool and dreary in winter, but reasonable during the fall and spring. Most of my plants do fairly well, even though they aren't in anywhere near appropriate conditions or locations. Due to the size of my yard and proximity to my neighbors house Ive had to do the best with whats available to me, but the yellows specifically have been a constant disappointment.

Yes, its S8 (Sugar Dragon). They were first out of the gate this year. The others are a few more 'heritage' white variety fruit, one of the plants I started with back in the olden days when I first started growing (4 years ago). It makes nice sized fruit but its the milky fleshed, kinda bland flavor. I have another white, one I got from growers out here in So Cal, that they started from seed by cross-breeding whites. They called it "K-Series", why I don't know, but its almost as sweet as some of the more popular varieties, good size and nice crisp paper white flesh. Those will be the next ones to ripen.

Don't remove the new shoots. When a plant sends out new shoots from its tip area, that usually means that the existing branch as hit the end of its growing cycle/length, and is pushing out its resources to new shoots to continue its growth expansion. Give them some time and see if they all mature into solid new branches, and then consider cutting back one or two, until the plant reaches its desired height. To be honest, though, its not absolutely necessary to cut back any branches this early, if you can get them to cooperate and train them to grow up your post to your canopy. 3 branches can mean 3x the new shoots when the plant is finally tall enough to start growing it back down for fruit production. It all depends on your growing style and your support system you've provided for the plant to live on. As you can see by the included picture, which is about 2 years old now, Im a big fan of letting the plants have some say in how they decide to grow

Its like cross breeding in most other areas. If you take 2 things with differing traits but compatible reproductive systems, what you end up with is a mix of various components of the 2 parents, but to varying degrees. Some traits can be dominant while others are easily suppressed. Often times it takes multiple generations of cross pollinating to get specific attributes like size, color, sugar content, etc. up to where you want them. Even Self fertility and self pollination are genetic traits that may or may not survive a crossing.
Also, regardless of what species you pollinate with, you'll always get a fruit that matches the flowering plants species. Its the seeds that get the new genetic code. You don't change the womb with new pollen.
Also Ric, the thing with cross pollinating creating bigger fruit is not on a genetic level, but on a abundant fertility level. The the only way I can explain it is that using another species' pollen actually makes the flower you put it on generate a bigger fruit, which I think is a result of more successful pollen acceptance, which generates more seeds per individual fruit. Like twins in a single womb. I don't know if this is fact or speculation, and Ive never experimented with this as I normally use a single species type of pollen for all my plants (as long as its available). It wont cause the seeds to generate plants that produce bigger fruit, unless that is one of the specific genetic markers that gets handed down from the chromosome paring.

Heres some images of the first proper S-8 Sugar Dragon of the season. This is about average size for the fruit, and good color. Brix score varies a little bit between fruit, and the 18.0 is a smidge low but it could be because it's a first flush fruit. Most of the plants make up for the small size by putting out larger numbers of fruit.

Artificial lighting should have little effect on pollination due to there being very little activity normally during overnight hours, as most plants that get 'assistance' by pollinators in the US (by bees normally) happens in the early morning when the flowers are still open and the insects are getting to work. The plant is naturally pollinated by moths and bats and other night insects in its native environments, but we don't have much of those types of critters in the US, as our varieties are either day shift workers or carnivores looking for bugs, not nectar. A nighttime camera shoot should be totally doable.
As for varieties, remember, theres a difference between self fertile and self pollinating. Self pollenating generally don't require any outside assistance to create fruit and are ideal for harvest crops, but as of right now most, if not all , of those varieties are not of sufficient quality to make a spash at market, although the work continues to correct that. Self fertile, however, makes up the bulk of the plants we 'hobbiest' growers own, due to the fact that most of us don't want to end up with a pile of dead flowers because we didn't have compatible pollen in time to fertilize what our plants see fit to produce. One important thing to note though is that location and climate can make self fertile plants into self pollinating, given a few things. For example, in a breezy or windy location pollen can work its way down the inside of a flower onto the stamen by being shook loose and basically just trying to fall out. At my house, if I find a flower I managed to forget to pollinate by hand, I always give it a good jiggle in the hopes that there is some pollen left inside.
Personally, Id prefer to have a better quality fruit that took a little bit more effort than a mediocre one that was completely hands off, but that's just me.

I have 10 DF in 15 gallon containers, with trellises. I have a question. I noticed today the one with the largest segment, probably 18" long and almost as thick as my forearm was starting to rot so I cut it off. The rooting segment plus the three sprouting from this big one look perfectly fine. Its the only container I have that's in morning shade only, the rest are in filtered sun all day long(it's  100-120 degrees here during the summer). I never moved it with the others because it was growing so big right where it was. Since it's in the shade I sparsely water it compared to the others.

 Do you think the fact that it spends so much time in the shade has anything to do with it rotting? And why might you guess the other segments look fine, but the biggest and greenest of them all is the one that got sick?

Was the 'rotting' area turning a sort of honey yellow, and a bit mushy? Possibly centered around a thorn point and spreading out length-wise in both directions? That sort of rot is usually caused by a bacterial infection in the soft tissue of the plant. It can work is way in under a thorn, or through branches banging against each other and piercing their skin with other thorns. I do not know the type of bacteria this is, or its source of spreading from plant to plant, but it somewhat common at my house, on certain species. On newer branches I cut away the entire stem, but on older growth I can successfully remove the infected tissue with a sharp knife and wash the infected area clean with a garden hose on a strong jet setting. As long as you wash away the affected tissue and peel away any remaining loose skin from the area, exposure to the air will dry up and harden the remaining exposed tissue and the plant will keep going strong. Remember, as long as the central, wooden core of the branch remains intact, the plant will have no problem supporting living tissue further up the line.
Now, as a side note, other conditions that can kill the tissue can also bring on this bacterial condition. If you have a branch that gets separated from the main plant or a whole plant that the root system goes into shutdown, the bacteria can start to consume the tissue as it dies, which can radically increase its spread. Its always best to deal with infections as soon as you find them. Even something as simple as poking a finger through a soft area to let the air in can change the course of a bout of this problem. The bacteria seems to be anaerobic, and shuts down and dries up fast when exposed to air. If you want, you can also add a anti-fungal/anti-bacterial treatment to areas once you've cleaned them, but that's a persona choice, with organic and non-organic options available.

its technically not a weight issue, but more of a maturity issue. Just like in most things, plants have to reach a level of maturity before they can reproduce, doubly so in perennial plants (as opposed to annuals). If you trimmed every offshoot from a dragonfruit plant and reduced it to a single branch, after a time, usually a growing season, that branch would have developed the chemical production and physical size to create the chemistry necessary to induce flower budding. You wouldn't get much in the way of fruit though, because you would be forcing the plant into an orientation foreign to its natural design. Remember, Mother Nature is a heck of an engineer, and has a way of making things work according to their environment.
Pitahaya is natively a climbing plant, working its way up the landscape to achieve a reasonable size for propagation, which it does in 2 ways:
1. Chemistry changes in the native soil, which correlate with the additional sun and rainfall of the spring and summer seasons, induce flowering, and then fruiting, in order to spread new seeds across the landscape. Sweet edible fruit encourage the process by getting animals to eat the fruits flesh and then deposit the seeds, along with some natural fertilizer, randomly in new places, through hard to digest seed coatings and spotty droppings. BTW, nature's way of adding flowering indicators to the soil is the return of birds to the area, which produce high amounts of phosphorus in their droppings, which gets washed from trees and leaves and into the soil through seasonal rainfall.
2. Branches of plants in low nutrient areas wilt a bit and break off, creating natural cuttings, which also bring new plants, although usually in a more limited radius, but something is better than nothing.

Im not sure what the weather is like in Florida right now, but here in CA, bud death like that is usually caused by excessive heat. We're starting to see some very warm temperatures right now and I expect to see a lot of reports next week about peoples buds and flowers aborting in large numbers. Not much you can do about the ambient temperature, but if you can manage some partial shade for the plant it might curb the flower loss a bit. You have to shade as much of the plant as you can, though, as the heat being soaked up by the branches is doing as much damage, if not more, than the direct sunlight on the bud is, basically raising the temperature of the entire plant structure to the ambient air temperature, plus whatever heat the absorbed sunlight generates. The pics you shared seem to be of a white variety, based on the corked edges and lighter green colored branches, and those tend to take less of a hit from sunlight induced heat buildup, due to the lack of dark pigment, but over time it can still play havoc with fruit production.
Of course, you still need to make sure you are watering more regularly now that its summer and that the plant has all necessary nutrients to produce healthy branches and blooms to start with.

You can cut the plant down to a single branch and still have it bear fruit, although you're not going to get much. The fruiting process basically boils down to a few key issues:
1. Fruit bearing flowers are almost exclusively formed on 'hardened' branches, which are last seasons growth, or very early same season, depending on weather conditions. These do tend to be more productive when hanging with tips facing down, but the "plant has to be XX size" is a myth in my opinion. It just needs to be allowed to grow and the branches to harden. I have a American Beauty cutting that I left in a pot and didn't stake it up, and its just growing like a Creeping Charlie plant, branches hanging over the edge of the pot, and in its second year its bearing fruit, without having to be run up a post first, then being allowed to hang. In my experience that is gravity possibly pulling heavier chemical triggers and pooling them at the ends of branches, which is one reason why branch tips, especially cut ones, tend to form fruit.
2. The entire plant is one big chemical reactor, converting nutrients, sunlight and water into the chemistry needed for growth, survival and reproduction. The bigger the plant, the more chemicals it can create, and the more it can spread around to other parts of the plant that might be lagging behind for various reasons, such as shade, disease or damaged structure.
3. Each branch, with its multiple thorn points (areoles), increases the chance of bearing fruit, just through shear number of available points to start new growth.
4. Proper nutrition can make even the smallest of plants (of proper fruiting "age") put out fruit like a champ. However, once you run out of possible new growth points, you basically stunt the plants growth, so make sure you keep a minimum amount of plant mass for continued plant development.
The basic idea is that if you let the plant grow a bit, you can trim it to a reasonable size, but you do need to feed it, water it (opinions vary on this detail) and, if you can, let it grow down in one manner or another, to give it a chance to do what it naturally does.