I can't speak to the limits, but 500 does not sound like a good idea. I had a form with about 20 sections and each section was fairly complex. It loaded reasonably well but I found that it was much easier to manage a single form of the BO that launched other forms of the same BO. This was actually quite elegant and you are never loading more than your largest form section, so performance is not an issue.
500 sections is a lot and indicates that you probably have many attributes in the BO. I believe that MySQL data rows are limited to something like 8k so you might have to be careful on that.
But if I was looking at the potential of that many form sections, I would almost certainly take the approach above - as I did with 20 sections.
