Circuit breakers Or fuses (overcurrent protection) are required to be withing seven inches of the power source. So the breakers between the batteries and the Battery Switch need to be close to the batteries. Same goes for the breakers off the main positive bus. (a bus is considered a power source.) I agree with the comment about cable size from the batteries to battery and to the negative and postive bus. This should be O or OO, or maybe 1 but definitely not 4.
are normally wired directly to the batteries with a bypass switch so you can turn it on and off manually. That gets a little more complex but when your boat is unattended you still want that pump
to come on if the bilge is filling up. Most boats sink at the dock.
circuits generally do not have a fuse or circuit breaker. The current draw of a starter
is so large it would probably pop any circuit breaker you put in the system. Plus that the only time there is current in the line
is when starting so there is really no need.
On the following page are links to sample wiring diagrams for various types of boats. You might want to take a look at them. New Boatbuilders Home Page - Electrical Systems
Also on the Alden Trull Web page there are schematics
for ten different boats. This may give you some ideas as well. Alden Trull Yacht Electrical Design