Ideally yes but if you can get a bargain then I'd rather go Enkei than some of the Ebay crap people have been interested in recently. On the other hand, I'd be interested to see what a trader like Envy charges for these new in more aggressive offsets.
As for size, it depends on what your priorities are - 20" for looks, 18" for performance, 19" a good compromise between both - IMHO of course.