Well, the back 5 are pretty much settled Casillas, Sergio Ramos, Pepe, Carvalho (Raul Albiol is out for awhile) and Arbeloa.
Khedira/Gago/L.Diarra/Xabi Alonso will vy for the two holding midfield type roles. Players play 60 games per season they all will play enough. Gago will probably be the least played midfielder. Granero will probably play also, with the other Diarra being sold.
Then you have Ozil/Canales/Kaka/VDV for the attacking midfield role, Kaka is out for awhile and I fear he won't play for much longer due to his constant injuries, Canales will be an impact player, VDV will probably be sold. Leaving Ozil in that role. Kaka doesn't deserve to be in the side anyway, his constant injuries have limited his play hence his average past two seasons at Milan and Madrid.
Upfront, Ronaldo/Di Maria on the wings with either Benzema and Higuain upfront. They might even play Benzema on the wing like he did at times for Lyon. Pedro Leon will also play on the wings it seems. But that isn't a problem as Barca have to fit in Messi/Pedro/Villa/Zlatan/Bojan in their attack somehow.
I don't see it being a big problem. Real Madrid have needed strength in depth and they finally have it, look at Barca, if they get midfield injuries, who are the replacements? They can cope upfront, but Iniesta/Xavi/Busquets/Keita is all they have for midfield. Probably the younger players will be called upon as they do every year.