Honestly, a lot of getting your setup right is going to be through trial and error. I think if you get a UTH that covers about 1/3 of the surface area, you'll be fine with one. Or, you could use two smaller ones. The 500R does have two outlets, so it would be fine to use two UTH on one t-stat as long as they are the same wattage. In theory, that will keep them at the same temp. I personally don't use any insulation other than the blanket on top of the tub, but my snake room is a little warmer than that. As for the top of the tub, foil isn't necessary as the solid lid holds in the heat and humidity. The nice thing about a tub setup is that it's pretty inexpensive, so you can afford to experiment more to get everything on point. And if it hasn't been said before, it's best to get your enclosure set up and stable before you bring home the snake. I'm glad I can help. I think it's great that you're doing your research and getting things set up properly. Your snake will thank you for it with a good feeding response and full sheds...