Approaching cars might think you're a motorcycle till they get right up on ya! If you could get away with a smaller, lighter weight, battery that'd be awesome. Maybe wire on a little solar panel to the battery to charge it during the day. There are companies that make small cheap flexible panels of varying voltage outputs.

On my old bike running a negative/neutral wire from the rear light back to the generator wasn't necessary because I could ground the light to the frame and it'd still work. Not sure if that will work if your setup but it could reduce the number of wires. It might reguire that you ground the neutral side of the battery to the bike frame. I think thats how cars are wired, and why all the neutral wires don't go back to the alternator or battery.