With quattro, you don't want to differ that much in wheel width between the front and rear wheels. The larger difference can result in damage to the differentials. A one inch difference in width is considered the maximum safest difference allowed.
As for the offsets. Many wheels with an ET32 offset will do nicely to push the wheel out to the edge. Depending on the tires used, you might need to slightly roll the edges of the fenders (if the sidewall on the tires is square instead of rounded).
I run during the summer a set of 19x9 ET 32 OZ Superleggera III wheels with no issues. If you have a big brake kit, you'll want to also check for caliper clearance (which could be resolved by using spacers).
Everything else is up to your own personal taste.