I don't know he would say to go smaller because you are considering a drop in the future. The problem is that with large wheels and stock suspension it'll look lifted. Don't get 18s unless you are going to drop it. 17s are iffy I guess, I mean the 7th gen actually has 17s on the 6speed and some optional 17's so it doesn't look horrible, but it always looks better with a drop.
If you don't want to mess with the suspension right now, don't go any bigger than 17s. Then if you do end up lowering it later, the 17s will still work, it'll just look a lot better.