I can get you a 17" X 5-1/2" wide wheel, direct swap-in.
17" wheel size gives the best availability of rubber, you should use the same type of radial front & rear. There are different methods of radial construction, mixing manufacturers front & rear could make your handling unpredictable if not unsafe. You can run a narrow tire on the 18" fromt rim, it's not optimal width, but it can be done. It isn't advised to go to a wider front tire than stock (using a stock 18" front rim, unwidened) if you choose to run radials, as radials need a wider bead measurement (width) to 'sit' on the rim, compared to bias-ply tires.
Generally, the 17" is welded-up and uses a donor rim, while the 18" is bolted-together and uses a new rim. Both are mated to the splined shaft-drive VMax rear hub. The 17" is $650 and the 18" is $1200. I have an 18" on-hand right now. PM me w/your email.