We still has enough experience with Pique,Pedro.Messi,Iniesta,Cesc,Busquets etc and Dortmund wasn't that experienced when they reached CL final last year
Agree. If Montoya is not yet good enough, train him to be good enough (they have till the end of the year and the pre-season to teach him as much as possible).
Although I wouldn't want Mascherano to go, but to move back to DM and rotate with Busquets (I know he'll have a much more important role is he goes to Napoli).
So I'd say sell Alves, Song, dos Santos, Afellay, Tello, Cuenca and Bojan and
buy the goal keepers, Benatia, another CB and Mattia De Sciglio (and Bruno Soriano - if Mascherano goes),
call back Rafinha and Deulofeu (wouldn't be good to loan him out again or he'll be out of touch with the team and gives Martinez a good chance to buy him)
and promote Denis Suarez.
PS: buying another midfielder would be much worse this time around than the Cesc/Thiago affair. At least Cesc was from La Masia and everyone wanted him back. It's not like Xavi, Iniesta and the likes had it all easy to become who they are today. It'd be too easy and not Barca-like to just buy
central midfielders and not look at La Masia or develop then like they've done until now.