RE: Kombat Differences
I really can't tell you too much about the Kombat 105/106/107 as the only Kombats I've owned and sailed are the 96 and 97, but to give you a "best guess" answer to your question I'd say yes, the boards will be pretty close in performance.
Since this will be your first really small board (I think) whichever one you can get the best deal on should be pretty much OK.
Just starting out on a board this size, you probably won't have the skills to notice or use the "nuances" that make the 105/106/107 different from each other.
There's going to be a bit of a learning curve down from your wider boards, but the Kombats are pretty easy to ride and I think you will find the transition pretty painelss, although perhaps a litte "wetter" than you'd like right at first until you get accustomed to the smaller and narrower board.
Hope this helps,