I would suggest you use multiples of three channels!.

As the supply requirements are well above that of a domestic supply you will need a commercial three phase supply - so it makes sense to split the channels equally over the three phases.

I would also suggest you use many more than three channels, that way the control systems per channel come back down to reasonable sizes.

A lot also depends on how far these lights need to be spread over - if it's over a long distance it makes sense to have a number of seperate control systems, perhaps linked together via serial connections, radio links, fibre optic links etc.

You really need to give far more details of what you are trying to do, not to mention considering the costs involved - which will be considerable!.