I think of alot of it in terms of pairings. So you have 2 centre halves and you need 3 good ones and 2 back ups for that pairing. I think we're ok there, we have the first 3 anyway. Then I seen Song-Arteta as a partnership that needs another player, someone like M'Vila, then you can have Coq, Diaby, Ramsey whatever as back up. Wingers is another pair sort of, so you need 3 quality players and some back up there, we should have Podolski, Theo, Ox, Gervinho, Miyachi there next season. Some argument on whether there is enough quality in that group but I'd say its not out weakest area.
After that you have individual positions in our squad RB, LB, AM and striker. I'd like 2 ready players for each of them and someone in a back role after that.
Guys like Ramsey, Ox, etc can do numerous back up roles too. That might be a reason to replace the likes of Djourou with someone a bit more flexible because he's shown a serious lack of quality at fullback. And Ramsey should only be a back up for centre mid positions, not the wings.