Appropriate Wheel Offset for 18" Wheels?

No, could get by with a 28-30mm offset front minmum on an 18x9. You will kick yourself trying to fit 9.5 in the rear, wont happen. 4 wheels at 18x9 with 30mm offset is lesser of 2 evils as far as front clearance, you will -1 gegree camber or more, and the smallest spacer needed in the rear.