There's a mixture of good and bad advice in this thread, which as a newbie I'm sure will be a bit difficult to navigate through. Some of it comes from highly experienced people, some from other relative newbies who really shouldn't be giving advice. As with any animal keeping community, you'll find a wide range of information in the herp scene ranging from brilliant to outright destructive.
Different things work for different people in different circumstances. There are different schools of thought when it comes to leaving a snake to settle in and offering it a feed sooner. I'm personally firmly in the offer it a feed immediately camp. I find that snakes are generally more willing to feed within 24 hours of arrival than if they are left alone for a week. When I was a newbie myself I followed the leave it alone advice, but after a few years of experimenting found it was counter productive. After quite some years of being in the routine of offering them a feed quickly I was chatting to John Weigel (I don't mean to name drop, just that this is an opinion shared by many people including one of Australia's best known and respected herpers), and he agreed with me, saying he saw it as a snake coming into a new environment and thinking 'Hey, this place is really good, there is food available here, I'm feeling happy' rather than 'Gee, I've ended up in this new place and it seems like a pretty desolate place with nothing to eat, I miss my old home where I got to eat, I really want to get out of here'. I might have added my own opinion there on top of John's, but that's the gist of how we both saw it. To give you an idea of feeding them unsettled, until about 15 years ago (I no longer do it because of quarantine concerns) I would let buyers bring back snakes if they were having trouble feeding, and I'd feed them for them. After a ride in a car, in a transport tub rather than their usual enclosure, and in view of two or three people, I'd almost always get them to feed immediately, almost always to the astonishment of their owners. At the time I think I found this a bit puzzling myself, because if I could do it with ease I assumed they could too, but I was instinctively using more technique than I realised.
I agree with smaller tubs being better, especially if you're not familiar with how to set them up perfectly.
40 is too hot. I keep the hot end in the low 30s, and ideally I keep the room above 20 for hatchlings, preferably above 25, so that the cool end of the tub stays above 25.
Pythoninfinite is an experienced keeper I respect, but I disagree with him on letting hatchlings cool down and 12 hours of heat being okay - not to speak poorly of him, but I think you'll get better feeding responses from hatchlings if you prevent them from experiencing temperatures below about 25 until they're established. Especially at this time of year as it is starting to cool down and the day length is decreasing, you don't want to be giving them any environmental cues to suggest that it's winter and feeding may be hazardous. Having experimented with many different things over more than 20 years, the best feeding results I have had are keeping them between about 28 and 31 degrees without having to thermoregulate. For various reasons that's not generally what I do for myself, but I see absolutely no reason for a new keeper to cool an unestablished hatchling overnight. Once again, I don't mean to say anything negative about Pythoninfinite, he knows what he is doing and his methods obviously work for him, but I personally would suggest you try a different approach. He obviously disagrees with me, you'll find a lot of that, that's fine and eventually you can see what works for you
This is largely personal preference but I personally don't generally like leaving feed in with them, I want them to enthusiastically seize feed from the tongs, 'kill' it and eat it. By all means have a go at leaving it in overnight, but I find it's wasteful (more often than not they won't eat, and every time they don't you waste a rodent, and they become familiar with rodents being a thing which they share space with which don't get eaten, rather than them being feed). There's a real knack to offering feed on tongs. I remember being a newbie and having trouble with it, and seeing experienced herpers doing it with some sort of magical touch which immediately illicited a strong feeding response. I can now very easily get many snakes to feed while newbies are completely unable to feed the same rodent to the same snake with the same pair of forceps. It's a talent you can develop, some people have a better aptitude for it than others. Unfortunately you've jumped in right at the deep end with a snake which isn't established and without first hand experience, but the good news is that it'll be a great learning experience for you. It is possible that your breeder fell for the trap of being easily able to feed the snake himself, but the snake requiring a skilled feeder to illicit a strong response. I always make sure that if the snake is going to a newbie it will immediately smash a rodent without me having to use any of the tricks involved with waving it around and strategically tapping the snake's body etc. I've also tried to find excuses to watch complete newbies try to feed my unestablished snakes to see what the novice buyers are trying to do, and I also try to find excuses to watch other experienced keepers feed tricky snakes in case there's anything more I can learn - we never stop learning and I still manage to exchange new tricks with other keepers with experience above and below my own.
Sorry for the encyclopaedic 'TLDR' post, and congratulations if you bothered to read it all! Have fun with your new snake, welcome to the world of snakes, and it gets a lot more fun when they're enthusiastically feeding