Since the small starters can't handle large let through currents of a short circuit on a 100A breaker (the contacts weld together), maybe you should put in a fused disconnect ahead of the manual starter that has the overloads in it for the smaller motor...assuming you're installing manual starters.
I've seen a lot of size 0, or 00, starters running downstream from a 30 amp breaker, even though the manual starter labels clearly disallow anything more than 15 or 20 amp short circuit protective device. This is a common violation.
