Not sure you will ever find a schematic for most any boat. Engine wiring, yes, but now so with most boats. However, you can remove the old corrode fuse block and install either another fuse block OR a circuit breaker panel.
As far as what fuse or breaker sizes to use, check what each circuit is doing and see the wire size and select accordingly. Not hard. Example, if your making a circuit for the bilge pump and it takes 5 amps to work it, use a 7.5 amps or something in that range or even a 10 amp will suffice. Reason why you go larger is because the inrush of current will most always be more then running current. However your wire size and current carrying capacity should never be exceeded (check wire size charts) and you don't want to go way over size either. And you don't want to fuse or breaker for the exact amount. JMHO
Do the same for each circuit and then you will know the needed sizes. Happy boating and post your results.
