17" Arc-8s don't look as good as the 18" variety, but they still look excellent. Everyone is correct in saying 17" tires will be cheaper. Definitely an advantage for someone who autocrosses. Have you looked into a set of 17" Kosei K1 racing wheels? They're inexpensive and lightweight. An autocross favorite.
Bilstein/Eibach B12 Pro-Plus Suspension & Sway Bars | DICE Mediabridge | Valentine One