That's no fun bud, not sure where the fire loops are, do know there are 4 fans in the forward electronics bay on the ERJ however...hmmm, i think.

To answer why systems are on different breakers, i'd say "redundancy" or "to aid in the system logic", cause odds are, it's for one of those reasons.

I wouldn't worry to much about busting a 121 check, you've gone through it before, you've passed it before, you'll go through it again, you'll pass it again, and when you get to said major, you'll pass plenty and plenty of checks over the span of your career. And probably bust a few also. Good luck, stay on the positive, and study up again, then show that examiner that you're a walkin encyclopedia of the freaking RJ.