It sounds like yāall really did your research when getting ready for him, so huge props to you. All of his enclosure specs sound really good - I personally do a hotspot 88-90 degrees but I know plenty of people do a little higher and have no issues.
First things first - how big is he? We generally measure ball python weight in grams and we also look at overall body condition (how they appear). I absolutely will say vets do know their stuff generally, but with exotics vets itās hit-or-miss and thereās a lot of misinformation out there that can be confusing to navigate. For instance, the breeding side of the hobby has normalized overweight snakes, especially females, and there are a lot of fat ball pythons in the world. We really donāt need to feed them in capivity as often most people do, but overweight animals have been normalized as the standard so many people may look at a ball python and see a āskinnyā animal when in fact itās very healthy. In my experience, younger snakes appear skinnier than adults for two primary reasons: they havenāt been eating for enough time to build up the nutritional reserve that older snakes have, and they also are new to the world so a lot of the bulk snakes get as they age is muscle raher than fat, and thatās something he will develop the more he grows. If you were able to weigh him on a gram scale (or if the vet weighed him and you remember the number) that could help us reassure you about his weight, and it would also be incredibly helpful if you were able to take a couple of pictures of him to show what his body condition looks like!
In terms of behavior, I donāt think itās worrisome at all that youāre not seeing him at the moment. The first couple of weeks he was there he probably did a lot of exploring around the enclosure - figuring out his new āterritory,ā exploring its boundaries, probably a bit stressed in a brand new environment which may have caused heightened activity. Now heās likely in the āsettling inā phase, which means heās getting accustomed to his new environment and resting. Iām guessing that the longer heās with you and the more you interact with him (cleaning, feeding, changing water, handling) the more you will likely see him out. The other possibility is that heās getting closer to shed, and when in shed they can be more reclusive, hide more, and be more grumpy. This should pass after his shed cycle.
I think the possibility heāll shed soon is pretty likely, given that youāve had him for five weeks and in my experies babies and young juveniles tend to sed once every month to month and a half. In shed I would recommend bumping his humidity up to closer to 70-80%, and you can achieve this a few different ways - I find itās easiest to bump humidity by pouring water directly into the substrate rather than spraying the enclosure. You could also create a humid hide - take one of his existing hides, put sphagnum moss under it and spray the moss directly so he has a higher humidity part of the environment with which to regulate his own humidity.
As for the pooping, I wouldnāt be worried about that either! Not only are snakes good at hiding poop (Iāve found it in some weird places) but if youāve got a bioactive substrate, your cleanup crew is likely on top of it. Snakes can get constipaed but as long as your temp/humidity is in the green zone itās rarely an issue. Also imporant to remember they have a much slower metabolism than mammals. My ball pythons will poop anywhere from once a week to once every couple of months. As long as you donāt visibly notice swelling near the cloaca or changes in behavior (lethargy, not eating, etc.) heās likely doing just fine. If it helps, I have around 30 ball pythons and I donāt track poops for a single one of them. 
Sorry, quite a long response, lol. Best of luck with your new pet! He sounds like a sweetie. I have a banana pied, too - a girl named Pandora. Iād love to see pictures of yāallās boy, and we can give you better advice about feeding based on the body condition as well.
