How many cycles does an ARM Cortex M0 use to multiply floats?
1 and 2: there's no hardware floating point unit on the M0, so it depends on your compiler alone. Expect on the order of tens to possibly low hundreds of cycles for single precision, with full IEEE compatibility. As for double precision, you're probably looking at high hundreds, maybe even breaking the thousand-cycle barrier, again assuming full IEEE compatibility.

3: single cycle.