You can do a search in the Suspension, Brakes, Rims & Tires forum. Lots of information there.
But to answer your questions briefly:
1. The wheel wells of the WRX are huge. You won't rub if you choose the correct wheel/tire sizes.
2. Larger wheel/lower profile tires will give you sharper turn in and usually better road holding. Ride will be a bit harsher. I am running 215/40R18 on 18" OZ Prodrive, and the ride is quite acceptable on most roads. 215/45R17 aren't that radical nowadays.
Anyways, when looking for aftermarket wheels, make sure they have offset of +50 or more. They are limited, and this is a price to pay for getting Subarus.
As for tires, go to Tirerack.com and look around. Lots of information. Many ultra-high performace tires now have treadwear ratings of 300 or more, which should give you a few years of driving.