as long as the transformers if low voltage are dimmerable theres should be no problem if they are mains voltage there will be no problem either.
yeah divide the total wattage by 2 and add it on will cover you ie 200 watts of light 300 watt dimmer 300 watts of light 450 watt dimmer you won't get dimmers exactly to the wattage you have calculated but just get the next size up