You only really need to have a breaker 15-20 amp depending on load on the positive so a single in line breaker would do fine. The you need an Electronics Master for all radios gps fish finder ect. highly recomend indivual in line fuses on each . VhF in transmit should be close to max. load, with others running. ADD total amp draw from all manuals add 20%. thats what you need. Try the web or west marine or boaters world.