He started 22 games last year which isn't bad at all, he averaged around 25 starts a season. Song can drop back into centre back but I remember Keita playing a left-sided role a fair few times so I'd say it's fairly even in terms of versatility but perhaps Song will just get more games ahead of the likes of Thiago more often than Keita did last year.
Release clause's are a requirement in Spain and the majority of them are completely meaningless, just absurd numbers. I think Ronaldinho's release clause is €200m in Brazil.
Christiano's is 1 billion Euros; they were thinking of buying him and Messi for 1 billion euros and 30 million quid, but decided to only go for messi!
Song'll be good for them; their squad seems to be stacked in terms of first XI, but has precious little in terms of experienced, quality players after that, and I really think they'll suffer if they get a few injuries.
At LB: Alba, Adriano and Eric Abidal (Still being treated, poor lad). Hardly much to boast about here in terms of cover.
CB: Puyol (Injury prone now, old etc.), Pique (Keeps getting dropped due to form etc), Mascherano (Done well here) Busquets (Midfielder); again, not much to boast about in terms of cover.
MF: Well stocked here, certainly
Attack: Messi, Villa, Pedro, Alexis (Iniesta). The rest are unproven youngsters. They are helped massively by the fact they aren't getting too many injuries to players like Messi, etc. but they certainly need to add 1-2 players in defence, and 1¬ attacker; or just hope no-one gets injured until a youngster integrates himself fully into the first team picture.
Obviously the fact that they are leaning towards 'pure' football helps them; each player ought to be able to play in any position (Bar Goalie).
However, in pure CB terms its shocking; they have Puyol Pique (Fontas). Luckily Mascherano's done well for them; and Busquets can do a job there.
Song definitely has a place in their team; he can pick a pass, comfortable in possession, big strong lad and is experienced and isn't massively expensive.
Arsenal losing another one of their better players.