Thinking about getting a bp but have a few questions...

[Craiga 01453]

Welcome to the forum, there's a lot to answer here, so I'll do my best....

Research, research and more research. You're off to a good start doing your homework beforehand.

Yes, you can keep your BP in the same room as you GPs. My snakes share a room with my ferrets and have never complained
I saw a mention of temp concerns with your animals sharing a room, mine do with no problem. It was also mentioned that an RHP or UTH might not be enough to heat the enclosure properly. Well, a UTH is for hot spot only and not ambient temps. So yes, you will likely need an additional heat source.

Read through the stickies on this forum and follow them. Whichever enclosure style you choose, there are stickies to help you get everything you need set up and set up right the first time. I use glass, for now, and have no issues at all, it's just a little more work. I will be adding PVC eventually, when funds allow, but have no issues with glass.
A 20 gallon would be fine for a while, and probably forever with a male, but I prefer 40 gallon breeder tanks.
You can easily cut a piece of cardboard to fit the screen lid, cut out a hole for your lamp/CHE (which you will need for ambient temps, unless your house stay above 78 all the time) and wrap the cardboard in foil. The foil keeps heat/humidity in, while just cardboard helps with heat but actually absorbs moisture, draining humidity.

If you're doing your homework on this forum you'll learn pretty quickly who the experienced, successful keepers are and you should follow their advice.