For the circuit ab initio I teach 15 deg AOB for the climbing turns and 30 for level and descending turns. As a general principal I think it is reasonable to limit bank angle in climbing turns.
30 deg's in the rest of the circuit allows for nice square corners.
Again as a general principal while I do not prohibit flap extension in a turn, I definitely discourage it.
The bigger issue IMO, is nor bank angle or flaps in turns it is teaching the judgement and anticipation so that the circuit works with the desired bank angle and the flight path is managed so that flaps don't have to deployed in a turn.
Sadly in lieu of emphasizing flight path management in flight training schools, we too often get one size fits all "rules" mindlessly passed down from one instructor to another.