I have Mach3 set up in inches.

My steppers are 200 steps per 1 rpm

My microstepping is at 8, so I have 8 * 200 = 1600 actual steps per rpm

I have 1/4 - 20 lead screws, so I have 20/rpms per inch

so 20rpm/inch * 1600 steps/rpm = 32,000 steps per inch

This gives me 32000 "steps per" in the motor config setting correct ?

Yes, that's correct.