Re: wiring diagram and questions
You don't need to reinvent the wheel.
Basic Battery Wiring Diagrams This is a very good basic primer for boat system wiring: Basic Battery Wiring Diagrams
This is another very good basic primer for boat system wiring: The 1-2-B Switch by Maine Sail (brings together a lot of what this subject is all about)
1/BOTH/2/OFF Switches Thoughts & Musings - SailboatOwners.com
Stu Jackson, C34, 1986, M25 engine, Rocna 10 (22#)