12 volt backup lights and heater take 9 amp fuses, almost all original 12 volt stuff is 9 amps except the 12V radio takes a 7.5 anp .....
if you use too high a fuse rating it may not blow when there's a fault - err on the side of caution, use no higher than 15 amp in anything unless it immediately blows on first use, than if you're sure the circuit is good [ohm check for shorts to ground], use 20 amp, but I'd say none of the things you list will need more than 15 except possibly the back ups depending on how big the bulbs are
let me emphasize that: caution is a
smaller fuse rating, it's easier to change to a higher rated fuse than to replace wiring fried because the over-rated fuse didn't blow in time
Bill
