Oh right, didn't realise you watched much Ukrainian or Russian football.
Unless you mean that you have just watched Willian in the Champions League, in which case you have seen as much of him as I have - and he is not as good as Rooney.
Not sure what you mean by Kagawa and Nani being just names, given that both have already shown they can be the top quality attackers you are craving. I think you are being particularly harsh on Kagawa, wanting to transfer someone else in because he didn't immediately come to a new club and start putting in world class performances. Have some patience.
Anyway, on your long and short - If Rooney stays he is certain to be a nailed on starter, whether that is one the left or centrally behind Van Persie. He was dropped for Madrid but lets not go overboard, he is still one of the first names on the team sheet and you're kidding yourself if you think he'll be frequently getting benched. As for the others I expect form will come into play, Welbeck could conceivably make the left wing spot his own, as could Kagawa. If Moyes looks to use a proper winger on the right you have Nani, Young, Valencia and Zaha all competing for one space - I agree none are guaranteed starters but any of them could becomes so, we just need one to step up and stake a claim.
I think we could possibly do with another winger, given our main three have been out of form. But even then it means at least one will have to leave IMO because there is no point having three or four sat on the bench every week.