my main switch is in the galley below the stove and my panel is next to the icebox. those runs aren't too long, maybe 12-15 feet but i wanted to be able to start the A4 with the house bank just in case, hence the heavy wire. works like a charm.
my start battery is in the old location next to the engine. the negative lead goes from the house bank to the start battery negative and the positive goes straight to the switch.
regarding the weight in the stern, its all you baby (and hopefully someone special)