As far as maintenance, I normally don't turn off any breakers while performing maintenance, especially the house breaker. I turn the controller to OFF and shut the gas off as part of my testing, I seldom pull the control fuse.
If I understand correctly, the fuse removal to the controller would prevent the controller from trying to initiate the generator if the power failed and it was inadvertently left on AUTO during maintenance. Turning the gas off would prevent the attempt to turn the generator on from being successful, but it would still turn it over a number of times using battery power. Did I get that right?
The last time I talked to Generac about engine oil I was told that the factory oil is non- synthetic to help with the break-in of engine parts and they like to see it run about 25 hours before it is changed. You are correct that it might take years to see 25 hours, in that time the oil will look like coffee with lots of cream from condensation in the oil. If you are able you can run the unit for some extended times to get some run time on it, loaded would be better, try to shoot for the 25 hours within a year.
This is the same conclusion that I had reached as well, I'll need to artificially increase the run hours to reach the 25 hour mark in the first year.
Valve lash has improved from the factory but I check and adjust all of my units each time I perform maintenance. I would not wait two years for the oil and valve lash.
I'm surprised you check the valve clearance each visit. It seems like there is significant disassembly required and the replacement of a gasket that is consumed during the process. You mentioned this is getting better over time. Do you find you need to adjust the newer machines at all in practice?
Thanks for your response, it is very helpful.