Giving Myself A Headache

I know that I'm overthinking this electrical stuff, but the simple awareness of that fact does not actually help me get any closer to a solution. I have been through several tribulations in my electrical approach.  Turns out that the bulkhead connector I was planning to use could only carry 5 amps. Not good when the marine VHF radio uses 5 amps by itself.  A more exhaustive internet search turned up a 5 pin connector that while more expensive can carry 16 amps. Newly confident I started looking at marine digital receivers, but came away disappointed since I would have to dedicate 15 amps of capacity for a small one. 15 amps not only loads down the connector but would also be a quick way to drain the batteries. Also being a mechanical engineer, I've never really learned to trust batteries. So I was hoping to have 2 batteries that I would use one at a time. Basically to give myself a built in warning when one died.  It looks like I will have to give up on that and wire the batteries in parallel so I can insure I'm running a common ground throughout the system (it was looking like I would need a 6 pin connector to do this in the one battery at a time way while keeping the nav. light switch in the cabin). . Finally I thought I would just run down to Radio Shack and buy some wire to get started, Ha. In my perusal of internet wisdom I found a PDF file on boat wiring (added to my links section) and learned not only about sizing DC wire runs, but also that the wire should be tinned copper.  With all this churn I was surprised to find that the schematic at the ama level didn't change. I will have one open pin in the connector but I kind of like that since it leaves some capacity for later additions. What I'm planning for wiring in the cabin is greatly affected, but I will worry about that when working on the cabin.