On a few but not all of your points, since all of them are very solid, I just want to give some commentary (if BP):
- I've heard recommended that you might want to go for the slightly taller t10 or t12 because the 12 inches of height in a t8 doesn't give you much room while cleaning. You can also give more climbing opportunities with a bit more height if you want.
- 55-65% humidity is usually what I aim for, 70% while in shed.
- If you're doing an AP enclosure, a radiant heat panel by Pro-products is the best option. They will ship it directly to APCages at your request and install it for you.
- I like to provide UVB/UVA because reptiles can see UVA, so just using a regular florescent/LED bulb means that a part of their visual spectrum is missing. They will also bask in the light if given the chance with UVB. It's not required, since they are a nocturnal species, but it's easy enrichment to give. Just add an extra light bulb! lol. If you do go this route, make sure the tube spans at least 2/3s the length of the enclosure, and give them plenty of opportunities to get away from the light or get closer to it. The flourescent/LED bulb can span the entire enclosure but that's just what I've researched for the UV bulbs.
As for suggestions, I do wish I'd known about Russian rat snakes before getting my BP -- I might have gone with that first if I'd known about them. Their temperature ranges fall right within my living temperatures (70 degrees to 82 degrees) and they're diurnal, and have a reputation as super curious/friendly. Usually get between 5-6 feet but they're pretty thin, being a colubrid. Either way, the choice is up to you!