3 600w or 2 1000

You can tandem lights on a light rail either add a bar or extention to accomodate them, the control is don't have the mover go so far that the primary plants go dark. You get better lower branch development too and can get closer as the light is moving. I run oscillating fans between the light and canopy to blow away hotter air. I get within 3-4 inches. I also would use either more fans or a stronger fan to exhaust the lights. If going vert a soft upward flow to let the hot air rise. Before you build post your blueprint. CO2 becomes less useful with some set-ups as it gets removed too fast.

I would go with 2 1000w. They have the best light penetration so you will be able to grow overall larger plants since the light will penetrate further into the canopy.