I'm looking to purchase new wheel for my 89 supra. i want 18inch. Just wondering whats the best offset to go with?

The offset totally depends on the width of the wheel, and if you go to the extreme outside fender edge the tire choice also. To give you an idea on a MKIII a 9" rim with a 32 offset will be almost flush front and rear. You could go with a lower offset or wider rims but you will have to experiment to see what you like the best.

Sawblades are the only rims you need for your MK III.