I got the new Toyota s12+8 calipers with the vented rotors on lst night. The slotted rims dont clear the caliper, probably by 1/8" or 1/4". But my question is how much of the wheel stud is needed for safety? Right now, without the wheel spacer, the wheel studs barely stick out through the holes in the wheel and the lug nuts probably grab about 1/2" of thread. Are longer wheel studs needed, or longer lug nuts, or is it safe?

As a rule of thumb, you should have the same thread engagement as the diameter of the stud. So in the case of our Zs, 12 mm of engagement. (Almost 1/2")

where can I buy wheel spacers? no stores in town have them...

check here http://www.thezstore.com