I'd buy Hummels. Kolo Toure will probably leave in January, so we'll need to buy a centre back anyway. Hummels is class and he's only 22/23. Him and Kompany would be first choice, but Lescott would still get quite a lot of games in the league and in the cups.
I don't think we need another central midfielder. When Toure goes to the African Nations Cup, we still have De Jong, Milner, Barry, Razak and Hargreaves. That's plenty imo. Razak looks good enough to fill in for a few games, interested to see him tonight.
We definitely need a fourth striker. But definitely not a world class player. I'd like a young striker. Try and get an unknown youngster e.g Hernandez, that'd be the best option. Even bring Guidetti back if they think he's good enough.
We only need to tinker with our squad now.