Those motors would have plenty of power for any of the machines you list above, with the possible exception of the merry-go-round (depending on how many horses it's got). Servos tend to run best at high speeds, so some kind of reduction would probably be appropriate, especially if you go with rack and pinion drive. Mach3 doesn't support closing the servo loop in software, so LinuxCNC would be a better bet for control software. If you want to be able to mill light metals as well as wood, plastics, etc. make your machine as rigid as possible, using profile rails and trucks rather than the round ones.