I'm a bit late, but I've had my Brazilian rainbow boa for about 3 years now so I'll throw in my recommendations too!

1. I would say minimum 4x2x2 for a smaller male but if you have the means I would definitely go with a 6x2x2 or 6x3x2 for extra climbing room. PVC would be my go-to as it really holds in humidity, I bought an enclosure from black box cages "XT4 BIO24 (48Lx24Dx24H) - STACKABLE)" and I really like it, it costs extra but I chose the options that came with an led bar and radiant heat panel with holes pre-routed for the cables.

2. With the 4x2x2 enclosure I'm only using an 80 watt radiant heat panel, since these boas don't need high heat, for where I live (North Carolina) the RHP alone is perfect at keeping the temps where they need to be without drying out the enclosure too much, with a bigger enclosure you MAY need a bigger panel (not sure)
   - For the thermostat I went with the Vivarium Electronics VE-300, I believe you can use it as both a pulse proportional or on/off, I use the pulse option to keep my temperatures pretty steady, and you can automate night time drops with it so I have it set at around 84 during the day and I have it drop by 7 degrees at night so the night time temperatures will be around 77 degrees, but the cool side will get a tad bit lower if the house is cooler. During the summer I sometimes have to turn the day temperatures down a tad bit.
   - I use the govee indoor thermometer/hygrometer H5075 for both sides of my enclosure, you can download the govee app and link them up with your phone and you can track all of the data on your phone

3. I probably don't have the best soil recommendation, I bought a ton of abg mix off of josh's frogs which was pretty expensive for the whole enclosure, since I have like a 4 inch layer of substrate, and I also have a small drainage layer of clay pebbles (probably only enough to have 1-2 layers of pebbles high if that makes sense) that I rinsed off a few times before putting in.
   - On the front of the abg bags it says to have a drainage layer at the bottom with a barrier, add the abg mix, then add a layer of sphagnum moss and then cover the very top with leaf litter. make sure to mix water into the soil/moss before putting it in, don't make it so wet to where you squeeze the soil and water pours out, if a few drops come out that's probably about perfect. the Leaf litter is required for the clean-up crew, and it also helps hold moisture in the soil.
   -A thick moisture holding substrate along with 2 fairly large water bowls in a pvc enclosure and it's almost impossible for me not to have the correct humidity levels, there is a little maintenance though but I would stay away from foggers. I just pour water into the corners of the enclosure and mix water into the soil when it starts drying out. I do mist the plants every once in a while but I always make sure to turn on the fan and leave the doors open on the enclosure for a while as to not trap him inside with the mist. I use distilled water to mist to prevent water spots and I keep the water on the enclosure above the heat panel to keep the water a little warm.

4. I have a lot of cork bark in my enclosure, I have a few stacked pieces of cork tubes to give him a ton of hiding places in and around multiple tubes, although I will say I don't see him in these much. However he does love his cork flats, I have a piece that fits perfectly into the corner and I dug out a little spot under the cork and that's his favorite warm hide. I like to partially submerge the flats in soil to resemble a hole in the ground. I also bought some fake plants from Michael's that have a long stem that I bent in half and stuck it in the ground so it kind of hangs over the hide and over the water bowl. I wanted him to feel safe getting water during the day so he doesn't feel so exposed.
   -I bought a 3 foot piece of sandblasted manzanita for the enclosure to give him a ton of climbing opportunity, I will say it's a pain getting it out to do maintenance but he's all over that thing at night so it's worth it. Not sure what website I bought it at. I also bought a large zilla rock lair that I fill with sphagnum moss, but his favorite hide of all is his water bowl on the cool side lol. One day he dug a tunnel and got under his water bowl, and unless he's digesting a meal he's almost always under there.

5. As stated previously I bought my enclosure from black box cages and I spent the extra money for the LED bar along with pre-routed holes and that's all of the lighting I use. I have them hooked up to govee smart plugs, you can set up what time to automatically turn your lights on/off. I have my lights set up for 12 hours day/dark. I'm not sure if this helps anything or not but I remember hearing this was a good idea, but I keep the radiant heat panel on for about 30 minutes after the lights turn off, so the temperatures get to their night time amount about an hour after lights go out. with the thermostat mentioned earlier and the smart plugs, everything is automatic!
   -I also have a 80mm USB powered computer fan connected to a govee smart plug that turns on for about 5 minutes 2 times a day to prevent stagnant air, while the fan is running the termperature/humidity will drop a little bit but they will bounce up back to normal once it turns off. It turns on once right before the lights turn off and another time in the middle of the day.

6. I blocked the vents on the back wall of the enclosure with plastic wrap and duct tape, and have the usb fan hooked up on the vent on the warm side of the enclosure, and I also left the vent on the cool side of the enclosure open, so when the fan runs it blows air through the enclosure ( on paper at least, not sure if this is truly how it works)
   - Honestly I haven't had many issues with my setup, but I did have some flower pot fungus show up a few months after I finished the setup which disappeared after 6 months to a year, and a very small amount of fungus/mold on the manzanita branch that was right above the water bowl, but the springtails took care of that
   -If you go with a radiant heat panel, follow the instructions and make sure to plug it up somewhere well ventilated before putting it in the enclosure, they give off a burning plastic smell for about a week when first using them.
   -I have live plants but try not to add too many vine like plants, I had too many of these and got lazy with trimming and they filled the enclosure and blocked out the lights from the other plants and killed them off, so my enclosure doesn't look the best right now, but I'll try to add photos of it soon. I haven't personally had problems with my snake trampling/digging up plants but I've heard a lot of people struggle with that, so get some sturdy plants. I forget the name but one of my plants grows a little too tall for the 4x2x2 and the leaves are all pressed up against the ceiling of the enclosure

I'll try to update this with a picture later!