You should have a main fuse right at the battery that sits between the battery plus terminal and everything else, except the big fat wire that goes down to the starter solenoid (and on to the starter). The battery is the only thing that is capable of melting wires and starting an electrical fire. All the generating circuitry on the quad is inherently self limiting and does not need its own fuse. That's why the fuse is always near the battery.

10 amps is a good fuse value.

Starters draw a lot of current. My 150cc quad draws 40 amps. Fifty amp switches are huge and expensive. So what is wrong with using the ignition switch? You turn it off and take the key. It won't crank without a key. If you don't have a keyed ignition switch they are cheap on eBay and easy to wire in.

 

I have come across another problem and maybe dirtboy you could help since you have the same engine. I seem to have no coolant flow. Yesterday after riding the engine seemed hotter than it should be and the coolant lines were cool to the touch. There r two bigger lines (1/2 inch) comming from the engine. One line from the top (opposite side of the spark plug) and one from the bottom on the other side. I have them running to the radiator. The top hose on the engine goes to the top port on the radiator and the bottom hose of the engine goes to the bottom of the radiator is how I think it should be. Above the top hose on the engine is a small hose (1/4 inch). Were does that small hose go. Does it go to the radiator too? It looks like there is a place on the top port of the radiator to run that small (1/4 inch) hose to. I am getting a water guage for it today to tell me how hot the engine is getting.