A little electricity 101.

With a 12 v system you need heavier duty wiring. Reason power equals voltage times current. As voltage goes down current goes up. For those mechanically inclined think of a hose. To pass more water you need a bigger hose.

Stranded verses solid wire. Electrical current actually passes along the outer edges of a wire. Above a certain level of current stranded wire if more efficient for the same size wire. For a simple lighting system it really wouldn't matter. But there is an actual difference.

Dolf cart batteries are what are called deep cycle batteries. They are designed to operate at a slow long term discharge rather than a high surge. Car batteries are made to supply a large surge to start a car. Deep cycle one are what you want for a power system. They will last much longer.

Hydrogen and charging. You are going to get it. But it is easy to deal with. Either put the batteries in a sealed room or containers. Think Rubbermaid totes. One not big enough. Use as many as you need. Drill holes to pass the wires through. Seal the holes with caulk or silicone. Run a sealed pipe to the outside.