Only you can answer this question. This depends on your goals, schedule, age, training age, recovery ability etc. If you plan on only training for hypertrophy for the rest of your life you probably could, but I imagine at some point any/all of the variables I mentioned will change. And lets be real here, its call BBB for a reason…its f****ing boring. I am running my third straight leader of BBS and I am getting to the point of real burnout with it. When I move on to Jokers and PR sets I will be ecstatic.
Do you mean assistance or supplemental? Assistance is stuff like pullups, dips, dumbbell press, and good mornings. Supplemental would be your BBB sets and reps. I assume you mean supplemental. How many reps are your missing and on what sets? If you are having a hard time on the last couple of reps on your last set, you can probably just grind them out with some focus and determination. If you are missing a few reps on your first few sets you probably need to stop, run 7th Week Protocol: TM Test and make sure your TM is correct.
This is usually explained/defined by what programming you are running. But remember that one of the core principles of the program is to start light. When in doubt just set it to the lowest in the range and build up over time.