You will still have to drop the car with 18's since the outer diameter of the tire on a 17 or 18 should remain the same. With a car like the Focus, I think 18's are a bit overkill for a daily driver. The sidewall won't offer much protection to the rim if you hit a pothole, and we all know Tampa streets are pretty rough.

I'd stick with a nice 17" wheel. Still gives the car a really nice look (particularly lowered) yet it will keep its practicality as a daily driver. Just my .02