From my research, you really shouldn't put any more than a 3mm spacer on stock studs. You won't be grabbing enough threads with the lugnuts with anything thicker. So either go big and get bolt on 20mm ones that have their own new studs pressed in, or don't do anything.
As for #1, no you should not run different offsets/sizes/widths on our AWD drivetrains.
As for #2, depends on how much you space the wheels out