Getting three to six all at one time would be a bad call. I'd do two at the most, preferably one with an established driver. I know a guy that did just what you wanted to, and ended up getting three routes. He then got a fourth, got a free PSA from the terminal for a fifth. Problem is, his drivers suck and he has two or three of his PSAs split in half running supplements because the people running them can"t handle the entire area. That's the fast track to completely losing your ass. Sad part is, he'll take on additional supplements just to please the terminal in hopes of having those sups turned into PSAs (as if any of those supplements will get converted to PSAs anytime soon...pipe dream).
Long story short, I'd drive for a contractor for at least 6 months so you can see that side of it before you buy in. I had the same aspirations, but after seeing the contractors getting screwed (thresholds raised incrementally, core zones being whittled away at) and seeing how the dudes under the contractors get screwed, it's just not something I'd be a part of. Some guys like it, and if you can find a reliable guy to work for you @ roughly 600/wk you'd probably be ok provided your volume is steady and good. Rural or urban? Distance from terminal? Lots of factors at play here.
The point is, you have the make the numbers work. Supplementals rarely benefit you. Dependent on the PSA you run them off of, you can either help or hurt your core zone. Factor in van availability, etc. and see if you can actually profit with a sup. The best scenario is to get away with running one van per PSA and not splitting it up. As soon as you split one PSA into a PSA and sup you can just watch your profit dissolve. At least drive for a contractor for a while to see what it's all about and get some inside baseball knowledge before you fork over any cash to anyone.