So.... I can't speak for everyone, I know some people on here have gone a little bit thermometer crazy, but I run 2 thermometers on my rack one in the top tub and one in the bottom one. Since heat rises I just make sure the top isn't too hot and the bottom isn't too cold. You can run one or two per tub, but I just use the 2 for the rack total, plus my temp gun.

That being said make sure to run your thermostat probe around the middle of the rack so you'll have the best chance for even temps from top to bottom.

Also, what thermostat are you running, and is your rack open sided or enclosed? An on off thermostat will cut power to the heat tape when it reads your set temp, but the temp probes can be a little slow to read. And if you have an open sided rack the draft can cause some fluctuation as well.

Hygrometers may be something you want in each tub, but still not technically necessary. I use the humidity probes on my 2 thermometers and cycle them through my tubs throughout the week, it gives me enough info to know if I need more humidity in a particular tub.

As for hides, cardboard boxes work, I use plastic tub/basket things from Dollar Tree and cut an entrance in it. Now I do use a soldering iron/wood burner, but the same thing could be done with decent scissors (not from the dollar store) and sand paper or a lighter to soften the edges. That method is super cheap and easy to make.

I've also gotten into the habit of drilling a very small hole in the corners of the tops of my hides to make sure that humidity doesn't condense in there and make the bedding/snake wet.

Honestly hides are one of the cheapest things you can make yourself. Literally anything that isn't see through and has enough volume to hold the snake will work. Up to, and including, the tops/bottoms of foam restaurant to go boxes. Feel free to be creative because snakes don't care what the hide looks like, only that it does it's job of keeping them cozy.