There isn't exactly a shortage of poachers so if you're playing two upfront then look for a target man to compliment them. Your midfield is fine and has some good options with Muntari, Henderson, Cattermole, Riveros (Sessagnon great impact player from bench) and you have two quality young keepers. Spend 90% of you budget on a decent left back and centre back with emphasis placed on the defensive side of their game. Cheick M'Bengué from Toulouse is the ideal fit for left back already and only gets better. Will set you back around 8 mil.
Turner is quality but I don't think much of Mensah, look for a solid left footed centre back - dunno if Vertonghen will go to you? Other choices would be Bassong or Dante.
If you have any budget left over then Ondrej Mazuch is a cheap and very capable back up for Turner (who becomes world class with time).
Champions league in first season is difficult but not impossible.
As for who to get rid of: Meyler, Ferdinand, Zenden, Malbranque, and virtually all the reserves except for Colback (train him right and he can be useful). Can't remember if they're on loan to begin with but McCartney, Nosworthy and Kilgallon are also must get rids.
Sell Zenden and Malbranque for whatever you can get, they add nothing to the team that you don't already have, are old and take up 30+k each in wages.
Hope that helps.