Rotor thickness minimum 4-piston KH?

I believe the larger question is: are you making one face thinner that the opposite side. If you were taking it down to .750", by removing the stock form one of the two sides, you could create a bad condition.

I know we're all smarter than that, but it needs to be said

I have NEVER found a rotor on which this was an issue. As long as the caliper "float" device has room you are OK, including pistons