Not trying to argue or anything, but I personally would actually think that if you're not lowering, 19"s are better than 18"s. I don't know if you'd look up too high or anything, but if the car isn't lowered, you'll have much more room for running fatter 19" rims versus someone who is lowered and would rub with the same wheels. Gives you some added security against rubbing, and you'll probably have more wheel options available.
VMR is a good source for CSL style rims. You can check out tirerack.com and plug in the specs of the car and they'll give you a nice list of all the rim sizes and tires sizes that should fit. They have pretty good selection, too. If you have a lot of money to spend, you can get some nice custom wheels from CCW, HRE, BBS, or something similar.
Just for the ballpark, your front wheels will likely end up being between 7.5 and 8.5 inches wide, with a +35-45 mm offset, and your back wheels will probably end up being between 8 and 9.5 inches wide, with a +45-60 mm offset. This doesn't have to be staggered. 19x8.5 wheels with +45 offset, for example, fit fine in the front and back if you want a square setup. Most things in that range should fit fine on a stock suspension.