I would use a disconnect for each motor with appropriately sized Short circuit and ground fault protection fuses for each motor. The 100Amp breaker is the short circuit and ground fault protection for the Feeders. In addition, each motor should have it's own short circuit and ground fault protection as well as overload protection. To answer your other question: nameplate rating is used to size overload protection. NEC FLA tables (430.147 thru 430.150) are used to size short circuit and ground fault protection.
