Others may disagree, but I've successfully used a single Cruise Commander to run 4 motors. I have a 4-motor sets of MTH Centipedes, MTH sharknoses, MTH F-3's and a pair of Atlas RS-1's that have run for years, each with a single Cruise Commander.
Disclaimer: I run freights of 10 or 12 cars, up grades as steep as 3.5%, but only for 30 minutes or so at a time. If you plan to run really long trains for hours at a time, your experience might differ.