I know you mentioned you just got him but any idea how old it is? My BRB is the same way, like yours he spends alot of time in his cool side hide. Mine never comes out during the day, unless i just put him back in from handling then he'll explore for 5 minutes and go back into a hide. Im pretty sure the BRB is a Nocturnal snake so most of the moving around would be done at night. I wouldnt worry about them. About you using an aquarium, most people here dont prefer the use of them, but if you have to do what i did and get some plexi-glass and seal off a good 3/4's of the screen lid. It will save you some money rather then putting out for another tank and will do what you need. Now after your able to keep the humidity in make sure to spray the tank at least twice, maybe three times a day. Like always keep your temps right as well.
As far as it being frightened by you, of course its going to be your 100x's the size of it. Frequent handling will help solve this, remember no sudden movements and not to smell like food, and that will help progress your snake to being able to be handled. Like someone else had already stated always give them time after feeding, dont handle them within 24-48hrs since there last feeding.
Oh and about feeding, you asked where to feed them. Ever since my first snake ever i have always had something separate to feed my snake in, some people prefer this some others dont really care. It helps them learn that not everything that comes into the cage (your hand for example) is food. I feed my snake in a Tupperware container about a foot round, you dont want something so big that the snake has to chase the food around plus keeping it close to prey normally initiates a quicker strike rather then sitting and waiting for it to realize there's food.