I don't think that Xavi will be able to change a lot in Barcelona right now. I am not against appointing Xavi the coach, but I think Barca could've got a more experienced coach. Because Barca hardly has the funds to player sign players and rebuild. So Xavi has to work with what he's given right now and has to get the best out of them. All I can say is I hope he does well with Barca.
In terms of experience, Xavi does not deserve to be Barca coach. Even though when he was a player he was an intelligent player it was very different when he was a coach. But I agree with your reasons it is quite reasonable. Indeed with Al Sadd xavi was so good, he was able to get 7 titles in just 2 years together. But Barcelona has a different climate, choosing xavi is a gamble for barca.
At the moment if you will be looking for qualifications then chances are Barcelona will not have a coach as the shoes are too big for anyone to fit in! AFAIK the club needs a person with Barça roots and knows what the club objectives are right from the start! Xavi not only being coach, has been a player before and an exceptional one for that matter and I think it will take a coach like him to inspire the current crop that's there to fight for the clubs lost glory and status. All I can day is all the best to the legend!!