I'm only going to step up to 18's. That seems like a good balance between appearance, cost (wheels and tires), and ride quality. The car will see a lot of highway and plain old general use. I don't it to be a corner carver. (I have my Mustang for that.)
You should be fine. Here is the chart for stock options. 45 mm offset will make them look even better. Check out tire rack, they got a big selection of aftermarket rims. Make sure to look at a weight of a rim, sometimes they are heavy as hell and will kill performance and mpg.
Thanks for the reply. I don't want to put a lot of money into the wheels, so nothing I'm looking at will be ultra light, but even so, there is quite a difference, you're right. Funny thing is, some that look like they should be lighter than others simply aren't.
Just to close the loop on this: I went with an 18x8 45mm Enkei Vulcan and 245/45-18 Verdstein tire. Calculations indicate this combo sets outward. 5" more than the stock ones. No problems so far, and they look good.
EDIT: Oh, and I gained only 1.5 lbs per corner over the 17" stock setup.