So the halides should be fine on 1 unit(DC8 that comes with it) for the day cycle and you can use the other outlets on there for anything that will be ran at night. Moon lights, fuge lights, etc... You would probably need either a DC4/DC4HD or a seperate timer for the actinics. A DC4/DC4HD would allow you to control your actinics and some powerheads.
Unless the actinics shut off when the 3rd halide is about to come on. It might even be fine with the actinics and the halides on a DC8(depending on how many amps the ballast for the actinics is pulling). I think the 12 amp rating might be when the lights are firing up. If the actinics are already on, then the halides come on one by one, you may be fine. If anything, you can call/email Neptune Systems. I've called them and got all of my questions answered. Not sure who answered, but he was a nice guy.
Sorry for rambling. I'm thinking as I type...