The 3 speedlight setup is very nice. I decided to go with 3 SB-700s - all used. I had an SU-800, but found it just a bit unreliable outdoors in certain lighting condiitons, so I picked up a Yongnuo trigger/receiver set and learned how to work with manual controls on the lights. Eventually, it became easy, but I wanted more control. I then started investing in the Pocketwizard FlexTT5 and MiniTT1 units - buying them (also used) one by one. I bought an AC-3 to create zone control of the lights and so far they're working perfectly.
But I'd definitely recommend going with 3 SB-700s over the 700/600 route. The newer interface is so easy to use that I don't bother carrying a manual in my bag. I lived in the manuals of my (former) SB600/800s.