I don't mean play him as a winger, but in his natural position you also have Nani, Young and Rooney who can play there. Rooney, Young, Hernandez and Welbeck up front. Nani, Young, Park, Giggs, Valencia and Welbeck can all play on the flanks. If one is naturally Rooney - I would assume up front - and Kagawa behind him, that leaves two spaces for all those players.
Young might play for England in that position, but Fergie's preferred Berbatov and Park over him there; I doubt he'll ever line up behind the striker for United beyond emergency circumstance. Same with Nani, at least not without experimentation first. Fergie's said next season will be Giggs's last, with his usual "never say never" addendum, of course. And Park played few games last season, and poorly. Those two will likely be eased out of the squad, if Park is still even there. So, I wouldn't say it verges on too much competition. In fact, I think another forward wouldn't hurt, with Owen and Berbatov out of the picture. But the priority should very much be with central midfield.
Anyway, let's see:
Valencia/Nani/Welbeck-----Kagawa/Rooney-----Young/Nani/Welbeck/Kagawa
-----------------------Rooney/Welbeck/Chicharito
A random game next season:
Nani-----Kagawa-----Welbeck
----------Rooney
Valencia, Young and Chicharito on the bench, but starting plenty games elsewhere.
I think it's a balanced amount of competition, the sort we had back in 2008. Remember when people were saying we had too many CBs at the start of last season? Well, look how it played out: Vidic out, Smalling injured, Jones erratic when not; and saved by Rio's miracle consistency and Evans's miracle resurrection. Injury and form are the variables which strike every year, us seemingly in particular with the former, so I wouldn't be worried about one player missing out too much.