2. On the power center there is a breaker with a red and one with a green switch. Are these the breakers for the generator and the land power line? Do I turn one off and then turn the other one on when i switch between generator and land line?
The breakers will control your 110v AC circuits. One is probably your main breaker, controlling all circuits and the other may be just your air conditioner.
They will not control the generator (your gennie does not require AC power), and you will not use them to switch between shore power and gennie. If you do not have an automatic transfer or change-over switch, then it was common to have an outlet in the generator compartment, into which you plugged your big shore power cord when you wanted generator power.
Onan mufflers are available from a number of places on the web. Just Google your model number and see what comes up. We recently bought a new muffler and a voltage regulator from these folks.
They are super helpful-
great folks who go out of their way for their customers.
Can't help you with the switches in the kitchen.