Minimum use of 16 lamp Badboy T5?

I don't need the whole 16 tube system yet, so in what manors can I use it pertaining to how many tubes are installed? It has two on-off switches. Can I use less tubes than a switch controls? Is there 2 ballasts or more (I think I saw 2 putting it together but I remember a lot of wires)? Can I use less tubes then a ballast controls? Can I use 6500K and 2900K tubes at the same time with the same ballast?

I use mixed spectrums in a BadBoy and so far just fine... Now I've got more BadBoy's and don't mix as much... but I did think about keeping a couple veg bulbs mixed in the flowering lighting...

Also I bought 2 seperate 8 bulb units... 2 switches each... even more control... and I can layout the lighting as 4x4 or 2x8... costs ever slightly more to do that but the flexibility was worth it to me.