ive had my PB for about 3 months now and he has not pooped yet its not uncommon and generally they will digest everything they can and only poop when they have an accumulation of matter that has no nutritional value to them and cannot be digested to urates or urine. my BP eats weekly. i wouldnt be to worried he will poop when he is ready. u wouldnt want some one poking u and saying cummon take a dump alreadyhe has probably urinated a few times and you have not notice the substrate would have absorbed it. some times you can see urates left behind which are white generally dry but can be a little bit sticky looking. i have read multiple places that you dont have to change your substrate for a few months at a time. i think thats rater disgusting because i change every 2 weeks and can noticeably smell and tell it is spoiled. i have found this site to be the best reliable source of herp info.
the size of the feeder you gave him is fine judging by the explanation you have given of its size.