Buying my first pet! - Boa Constrictor - How to heat?

How do you guys heat your boas? I know there are a lot of different ways, I think I have heard that under the tank heat tape is practical. I am curious about an incandescent bulb, that seems like it could be more effective and “natural,” but I have also heard that can tend towards drying out the enclosure. I found a radiant heat panel that I can build into one, any of you guys do that without having to make up for lost humidity?

I am also thinking of getting a 3-foot-long enclosure with a long-term plan of stacking (side by side of course) two more, 3-foot enclosures, for either a common or long tailed boa constrictor. I am willing to be persuaded into changing that plan into two 4-foot enclosures which would be cheaper overall. Right now though, I would like to see my enclosure long term erring on the side of too long, having a cheaper startup (I will be spending tons of money on my new girl!) and purchasing 3 feet 3 times just sounds more maneuverable to me. I want to see my girl have as much surface area as I can give her, but it doesn’t seem advisable to go any deeper front to back than 24”, or any taller than 17.5”.

Which brings me to thermoregulation. I’d be surprised if I needed more than one thermometer for a 3-foot enclosure, but maybe that’s something to buy along with each additional 3-foot enclosure? I’d be willing to by a temp gun at the start to facilitate my first-time experience of creating a climate, paying extra attention in the first weeks. Is that overkill? I’m kind of confused how a thermostat hooks up to a heating element. I’m sure it depends on what I get, but is it generally pretty easy to “connect” them to each other? Do you guys prefer on/off over rheostat? Rheostat sounds better theoretically, but I guess on/off is better for your utility bill? I suppose a thermostat is the biggest potential threat to my pet. I am willing to pay for high quality but it seems high quality thermostats are all for breeders, not for just one boa. Any recs?

A thermostat is for a single animal keeper or a big breeder. The peace of mind and safety found in using them is always worth it. As far as heating goes, I use to use heat tape a lot. As I've grown older, and I like to think wiser I prefer radiant heat panels. I've got both Reptile Basics heat panels and pro products heat panels. Both work well, neither seem to cause problems with my humidity either which is good. Regarding thermometers you can find multi packs of "aquarium" thermometers for rather cheap on amazon and other websites.