My research indicates that the most expensive part of kitting up is rebuying gear. I would be very surprised if you were inclined to rebuy after getting a good BP/W, good reg set, especially Apeks, and a Shearwater DC. I did the AOW and buy dive gear thing this past summer and I am very happy with what I bought. I will also say that OW and AOW don't tend to teach much in the way of how to select gear - as you probably already know, that is knowledge one has to seek out oneself. The only thing I would add to the DC discussion is that BP/W setups work best with the DIR primary donate reg setup that tbone pointed out. That means you don't have a depth gauge (no console). That is fine, because your DC is a superior solution to your depth gauge needs. However, it is always good to have a backup. You could use your freediving Mares for that and be set. However, if you are going to be traveling for diving at some point you will eventually want a backup dive computer to your nice Shearwater. If you are getting up against your budget you could purchase your backup DC now and defer purchasing a Shearwater. The downside is that $200 backup/basic DC's do not run the same algorithm as a Shearwater. Until the Deep6 DC comes out (could be a while) that is just how it is.
I will also second the desirability of dry suits, with the caveat that I can't afford one yet either. One of these days...