To answer your questions, I have 3 AP cages and a Proline cage. For my AP cages, I use flexwatt only with herpstats and it works fine. I have the herpstats set to 95F for my BP which gives around a 90F hot spot inside the caging and I have my boas set to90F on the herpstat which gives around 85F or so. They like it cooler. For my Proline, I use a Pro Products PH3 65 watt RHP on a herpstat and that works fine too. So either will work fine assuming your house temp is kept 75F+. If not then you might need to add a RHP to help bump up the air temp inside the cage. I personally wouldn't add screen on top for a CHE dome as that will kill the humidity. I use less than 1" of aspen for the UTHs which works fine since the snakes will push the aspen aside if they want heat. I also use RBI hides for all my cages and they work fine as well.
PVC is easy to drill through so mounting a t-stat probe should be easy. I use the UTH simply so I don't have any wires inside the cages. I also opted for the LEDs they install, again so I don't have any wires inside the caging. I learned this as my big boa girl would yank down and kind of wiring inside the cage when she was hungry and destroying stuff.
As for sealing, I sealed mine inside the house and it was fine. It smelled for the first day, then after that it wasn't bad. It took about 4 days for the smell to completely go away. The snakes didn't seem to care but I waited those days before putting them in. I would avoid breathing it as it does contain toluene which isn't good to sniff but again, it wasn't terrible and this was sealing 3 cages at the same time so if you are only sealing 1 cage, you probably will vaguely smell it.
Good luck and I love my AP cages. They are sturdy and AP definitely pays attention to the details like smoothing any rough edges and stuff. They did miscount a few screws though as I ordered all of mine with shelves, locks, leds and flexwatt but when I mentioned it to them as just a FYI, they offered to send me more screws. Wasn't a big deal for me as I had that size wood screws laying around and just used them in the back of the cages where you wouldn't see them anyways. Just nice that they offered to actually send me the 4 total screws that were missing from all 3 cages combined.