Well, the solar really wants to connect to the house battery - that's what the solar needs to recharge. You'd normally connect the batteries with the switch when going down the road so they all get charged, then open the disconnect when camping so the starting battery doesn't get discharged to where it won't start the engine.
The wires are there for the generator electric start and are connected to the starting battery so you can still start the gen and recover if you've drained the house battery. They're probably reasonably heavy gauge, but better check and there may be a need to run heavier ones as your system grows.
Generally, you want the inverter as close to the battery as possible - a 400W one is going to pull over 30 A DC. Without knowing the wire gauge, not much can be said about what to expect.
