You do not need a switch between the regulator BAT terminal and the battery. The cutout relay in the regulator takes care of that function. You DO need a ground wire between the regulator base and the generator housing. That is absolutely necessary- - - -no discussion.

However, you don't need anything in the way of a charging system. Just use the generator as an idler to run the water pump with no wires connected to it, and connect a battery charger during the engine run. The KISS principle applies here, like in a lot of other situations. The engine will run on nothing but a fully charged battery for at least 6 hours, even without the battery charger.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!