Generally, whether waterstones or other, you need three stones. One coarse, one medium, one fine. for waterstones, it would translate to one 220-240 grit, one 1000, one 4000-6000. You could fudge it a bit with a stone in the 200-300 range and one in the 1200. This will leave you with a very nice EDU edge but still handle most any job that comes your way. You could also fudge a bit and just get a 1000 and a 6000 - will leave you with a good maintenance and finishing system - can add a rougher stone for repair and changing angles etc.
I make and sell a pretty complete kit for freehand sharpening through the link in my signature that might be useful to take a look at - have two left and probably won't be making more till after the Holidays. Its inexpensive and very functional. Otherwise, there are a lot of waterstones in the mid price range, most of which I have little experience with unfortunately. I own Kings and Norton, would recommend the Nortons as they handle a wider variety of steel - the Kings are a nice stone for the money but can struggle on a lot of the alloy and higher carbide steels, much better for carbon steel.
You could also start out with a Norton silicon carbide combination stone (Crystalon). It leaves you with a fairly rough edge, but as a stone to learn on you'd be hard pressed to find a better option - good feedback, handles any steel, predictable, consistent results, and inexpensive.