i would think that multiple circuit interrupters is overkill, but it's not really going to hurt anything.
the critical thing is for your interrupter to be rated to trip BELOW the current carrying capacity of the wire gauge you're installing. otherwise, you might burn the insulation off of the wire ( that's a fire ) and never have a fuse blow or the breaker trip.
see this page for reference:
i wouldn't route anything lighter than 12ga. and while 12ga / 30Amp should be fine for something like a car stereo ( which is rarely going to be over 50% duty cycle ), if you're wiring phone battery chargers, etc, those are going to be 100% duty cycle while they're in use.
that's going to put a lot of heat into the wire/insulation and so you're going to want a breaker on that that's under 10 amps.