Depending on what your climate is like you don't always need to worry about humidity as much as people do. Except during shed. You can always bump up humidity to help for shed. You don't want to be over misting either. Hydro gauges aren't always accurate either. Most of them are crap. I can't remember which ones go with the kit but I they are the little circle ones or the plastic strips they are junk. And don't use the temp gauge of those at all. You need to know the temp right above the heat mat, not on the side of the glass. The heat mat can burn your snake not the ambient temp.
If your Bp is small the 10g will work but thy do grow out of them pretty quick too.
If you bought him on the 18th you shouldn't have tried feeding him yet. When you get a new snake you let them settle in for at least a week. No touching and you don't need to feed either.
Don't have damp moss in his hide unless he is in shed. Such an included area could have humidity 90% in there.
You are on the right track. Just need a little tweaking and a little more research. You already said you are getting a new thermometer which is good. Do that ASAP because you gauge now might say 90 give or take but your mat could be 120 or more and that is bad. Even with extra substaright on it the snake can always burrow down. Keep up with how you are going and you'll get it perfect pretty quick it sounds.