Baby BPs feel insecure in a large space. Since tubs are cheap, you can buy little ones and move up as the snek grows. If you really want to start with a larger one, buy a bunch of silk plants to clutter it up. Baby BPs feel a lot more secure when they can hide in the plants. After all, if they didn't hide well enough in the wild they'd be dinner pretty quickly, and they still have their instincts! Some species don't need hides once they're adults, but BPs are naturally inclined to cram themselves into a crack under a rock so they do like tight spaces.

I'm not aware of any heat mats that have reliable built-in thermostats. As already stated, a Hydrofarm/Jumpstart is a good beginner model. Best bet is to get a digital indoor/outdoor thermometer, and hot-glue (don't use the provided adhesive. Snakes are good at getting stuck to things and that tears up their scales. No sticky stuff in the enclosure!) the "outdoor" probe right over the heat mat, to make sure the thermostat is doing its job. Then also get a temp gun to monitor the rest of the temps.

You're gonna need to find a reptile vet. It's not a disaster if you don't get a new guy in for a checkup, but if your snake gets sick you don't want to be frantically googling and picking some random shmoe vet in a hurry. You might have to travel a bit. But definitely find out where you can go BEFORE something bad happens.

Oh, yeah, get your rodent situation hammered out before you get the snake. It turns out some moms aren't too fond of having a bag of dead rodents in the freezer or a cageful of live rodents in the house .

Females get bigger, and are less likely to go on extended food strikes. If you want to breed, get a female first. Other than that, not much difference.

Are there any reptile expos in your area? If so, that's a good way to buy a BP. Usually prices are lower, and you can see them before slapping your money down. If not, just take your time, find out who's offering cinnamons online, compare prices and quality, then google to see if that seller has any complaints, etc. There are a lot of really great options now so you're not limited to one or a few. Of my snakes, I got one as a private re-home and one at an expo, so I don't have any personal experiences with buying online.