Yah, it's amazing that homestead is so productive given the soil (or lack thereof). I have a remotely similar situation where I'm at. The original plot here had about 3 inches of top soil on top of about a foot of crushed limestone. My situation is not as bad as that of Homestead, as there is no hard pan to prevent drainage, and I don't need heavy equipment to plant trees. However, it was an issue that I needed to deal with. Here's what I did:
On one side of my plot, I raised the soil level by about 9 inches of solid black "muck" -- the result of a decade worth of heavy mulching. That combined with the original 3 inches of top soil left me with roughly a full foot of top soil. As I've discussed on other threads, growing in heavy organic matter has a couple of drawbacks, namely super high phosphorous, too little calcium in relation to potassium (manifesting itself as fruit with low brix and soft flesh), and a worsening chlorosis due to OM locking up micronutrients. I've been able to rectify both issues by fertilizing with various calcium sources (literally tons of it) and by fertilizing with micronutrients. The nice thing is that the organic matter tends to retain what I put down. So, it needn't be an ongoing thing. OM acts like bio-char, in that it becomes a reserve of nutrients once "filled."
On the other side of my plot (purchased about 4 years ago), I didn't feel like waiting a decade nor spending thousand of hours worth of labor pushing mulch piles around. So, I trucked in loamy sand from Palm Beach County. That was one of the best decisions I made. It came out to about $12 per yard, and with 250 yards, I was able to raise the soil to nearly a full foot above the limestone. I've subsequently been mulching to add organic matter and encourage beneficials. Since it is still mostly sand, I've been fertilizing that plot more heavily than the "muck" lot.
The trees on both lots look phenomenal, in stark contrast to those of my neighbors. With a bit of sulfur, I've even been able to lower the pH. Even though it's essentially impossible to lower the pH on the limestone that lies beneath everything, I can keep the foot or so of topsoil at a pH below 7 with infrequent (eg, once per year) sulfur applications.
The TLDR version is -- if you can simply build up about a foot of topsoil, you should be able to grow successfully, even on top of solid limestone. The only thing you'd need to deal with would be the lack of drainage due to the hardpan below.