You don't need to remove the fork guts to drain the oil, just take the legs out of the triple clamps and leave them upside down in a container (with the caps off) for a fair while to let as much old oil as possible make its way out.

The rear seems to benefit from as much ride height as possible but i don't think maximum preload is necessarily the way to go. You want only a certain amount of static sag for best results with the preload - you'd need to read one of those setup guides where they get you to measure sag under just the bike's own weight and then with you on it to see how much preload you need. Same goes for the front end. The adjustment will depend on your weight and how the bike gets used: on the road or track for example.
_________________
After years of moaning about immigrants now i am one...