That is my plan as well, no sense in void the emissions warranty until it dries up. Good plan to focus on the wear items like suspension, bushings, tie-rods etc first because they get used every single day you drive it and will actually help/improve the way the tune translates to the road when you do go down that road later.
I run 16's for winter driving, having a little more meat on the tire helps cushion the ride a bit more, they are generally cheaper and finding 16" 5x112 steelies for $25/wheel is also relatively easy. For summer I stick with the 17" 225/40/17, a little less cushion in terms of sidewall height compared to the 16's, but again it's cheaper to find 17" tires than it is to find 18". Performance wise unless you are tuned, lowered and ready for track days you can get the same amount of performance from a good set of 17" wheels/tires for less than you would spend on the 18"+ set-ups. Just my two cents. Also keep in mind that a lot of people tend to swap their. wheels when hey purchase Audi/VW vehicles and selling the old wheels as "take-offs" are pretty common. I know here in SLC, UT there are pages of stock "take-off" wheels in the classifieds for between $200-$400. Even if they have some curb rash or other imperfections you can take them to a wheel shop and have them re-finished and/or painted/powder coated and they'll look new.
Lot's of options either way you go, just take your time and do your research and it'll pay off.