MA is a strange state, lol - you can have an amethystine python, but not an ETB or GTP.
Even large amethystines will take advantage of perches or sturdy branches, so if you have the space they appreciate the extra height. Be careful about that though - as a rule, I try to keep them lower than my head...a large snake in a superior position can be a pain right in the butt.
I don't know that I agree with the statement that they are from low humidity environments...actually, I don't agree with it. Sure, the range is wide, and they can be found in very dry areas, it really isn't the norm. Amethystines actually move around quite a bit, and in the cooler months will head to the valleys/flatlands where they can better thermoregulate. In terms of husbandry requirements, they are fairly forgiving. They can tolerate a fairly wide range of temperatures and humidity. For temps, shoot for the standard 80ish cool side - 90ish warm side. Humidity, as I said, they are pretty tolerant, but I always shot for 50-60% RH. In a large enclosure, you will be hard pressed to get it higher than that anyway, without automatic misters. If it drops lower (as it probably will during the winter), an occasional misting or a large container (of water) to soak in will do the trick...esp around shedding time.
VPI's site used to have a page with info, but it seems to be gone. I would think that their first book (Pythons of the World, Volume 1, Australia) should have plenty of info on amethystines. I spoke with them quite a bit about these pythons a number of years ago.