If Barcelona had bought Cesc, they would be stronger to win a Champions League. However, in another point of view, with the permanence of Cesc makes Arsenal stronger. Concluding, I prefer that Cesc stays at Arsenal.
x2 Dzeko or Vucinic in Chelsea would be great. If Chelsea don't sell any player, they just need to buy a Attacking Midfielder Center. However on the next season, a forward and a back center must be bought.
Ozil in Chelsea would be perfect. He played very well in the World Cup and like you said, wouldn't be expensive. However, there are several teams with the same objective. I read that he already has a verbal agreement with Real Madrid. By the way, how Chelsea played at second half?