4 or 6 color press help!

I'm looking at a couple vastex units right now. Space is a factor but I have to think about the artwork that my artist will be making. I'm currently looking at the vastex v1000 unit, either with a 4 color or custom 6 color. I guess it all comes down to the art work and how we want to go about printing the shirts.
I only print on dark thin shirts. Since the shirts are already thin, I am weary of doing plast. Simply put. If your using a really thin dark shirt for production, what would be your recommended ink method? And how many colors would you feel you needed on an everyday press, note size does matter, 6 would be the most I could do. I was thinking discharge on simple designs. But what happens if I run into a little more complex design? Do you use plast or water. Spot, cmyk or process? Simulation or sub dye? Please help so I could get on my merry way.