For ZA, I'd say a minimum of 1800 healing and 200mp5 while casting, unbuffed. That's it you're trying for the timed loot, Hex Lord, and Zul'jin. Early TK/SSC should be around the same. By the time you're ready for Hyjal/BT, you should be running more like 2000 unbuffed and 250mp5 along with the 2pT5 bonus (shoulders + gloves being best imo), and could probably get higher.
For health, it really doesn't matter. You need stam-heavy pieces to switch out on certain fights (Zul'jin, Doomwalker, etc), but it shouldn't be an issue overall (my guild leader and our best healer, until recently, ran around with about 7k fully buffed in TK/SSC). Once you get to Hyjal/BT your health should already by higher, I've heard that you should try to run 9-10k fully buffed but only a handful of fights really *need* the extra stam (Naj'entus, for example).
Your mana pool doesn't matter. As long as you're not equipping +heal greens, it's high enough. Regen is what matters in raids.
For resistance, the third-to-last BT boss requires 295 unbuffed shadow resist, but you can't really get that without already being in BT anywho (crafted gear using drops).