Ignore lip size. You can run a 45mm wheel and 4" of lip and it'd look deep but not stick out far.
Offset is how far in or out the wheel sits on the hub. You can google it. Don't get it confused with backspacing. Similar idea, but backspacing measured from teh hub to the edge of the wheel. You need ET 20. You can run an ET20+ but it'll require a spacer. I run ET10 or ET15 17x10" wheels in the rear.