Mark, do you know roughly how much sand you are using?
Too much cause moving it from tractor's bucket to inside the greenhouse gets old real quick! If I had to guess it's about 30% sand and 30% coarse vermiculite or perlite, the rest organics. Even after 5 years the big pots drain really well.
I started off using well water which is very hard, TDS over 800 ppm, bicarbs of Mg and Ca. Neutral pH though. I now collect rainwater and use a cheap pump. Trees love it.
Speaking of trees, I'm VERY careful about my real estate, actually there's a bunch of wasted space but knowing that avocado trees grow big I give them plenty of room. I have 4 avocado trees, 3 citrus, 3 mango and a bunch of pineapples and misc. on two perimeter benches. If you like avocados a Reed is a must have. I have the best of the best some as individual trees, some as a cocktail tree - Reed, Oro Negro, Sir Prize, Holiday, Pinkerton, Ardith, Gwen.
Waldo (my wife is in that Reed tree somewhere).
Also, a VERY important consideration - you must provide for easy access for pollinators in the spring. I have hundreds of different species of bees, wasps, moths, butterflies and flies pollinators every spring. They get confused by any covering that restricts UV....can't find their way out.
BTW, your house is gorgeous. Mine always looks like a train wreck, leaves all over the ground, but it works!