Formation when we have ball posession (86% of the time)
---------------------------VV---------------------------------
A------Pique--------------------------------Puyol----------AB
L------------------------Yaya--------------------------------I
V-------------Xavi-------------------------------------------D
E----------------------------------------------Iniesta-------A
S--------------------------------Cesc-----------------------L
----------------Messi--------Villa----------------------------
Imo we do need a holding player in midfield. When we attack, our full backs, as we all know, tend to bomb forward and provide enough width. That's one of the main features to our game and we should really keep it. Pique and Puyol will push out wide with the holding midfielder dropping back 5 to 10 meters into the hole. That's the main tactical asset to our game. Xavi should just keep on playing as he is now. For the rest I would let the player's intelligence decide the attacking play. Messi, Cesc, Villa and Iniesta are all smart enough to know for themselves how to break down opposing defences. They know the passing patterns from training, are so technically superior and can apply all their vision, flair and creativity into any attacking role or position really. Let them swap positions a lot adn give them a lot of freedom. It will utterly confuse defenders. They won't know where the danger is coming from.
You can easily rotate things around and bring Ibra, Bojan or Pedro in. Every attacking player we have is so versatile.
Off course, when we don't have the ball, you will need to provide clear instructions as to pressing etc.