It depends how you want to set up. Brazil, for example, can afford to use two fairly limited players in the holding role, which allows the forwards to not have to worry too much about defending, although you'll notice that Dunga still uses either Elano or Dani Alves further forward with the clear intention providing extra cover. That also then allows the two attacking fullbacks to get forward, which means that six players can be attacking at any one time.
However, Brazil don't really use wingers, and the three players who float around behind Fabiano (Kaka, Elano, Robinho), along with the two defensive midfielders, afford them good control of the ball in the center of pitch.
But the point is that no matter which players we have, and which system we use, there has to be a coherent idea behind it. Sometimes fans get a little carried away and suggest that we should be using two attacking fullbacks, two strikers, two wingers, and an attacking midfielder in a two man central midfield, which is something that no other team in world football attempts to get away with, as far as I am aware. That's clearly not going to happen, so we have to make certain sacrifices.
Ozil, or a player like that, playing behind Rooney, would almost certainly mean that we should stick to using two fairly limited (in terms of creativity) central midfielders in Carrick, Fletcher, Hargreaves, etc. The difference between our system and Brazil's would be that their main attacking players all float around behind the main striker, whereas two of ours are not really comfortable in that position.
The good thing about a player like Ozil is that you could afford to bring on another striker during a game and either allow to continue floating in behind or to replace a wide player that hasn't been effective.
