Well, GK spot is saved for another 5+ years. Plus, we can have one of our young'uns be backup to Valdes no problemo I think.
We can save tons of money by buying Nagatomo this summer instead of Coentrao or Bale (assuming he's an LWB) for the LB spot, assuming he doesn't go through with his loan at Inter after the summer. It will be foolish to ignore him over a more expensive European equivalent when he can do their job for 2/5 of their price while at the same time being as effective than the others ever will be. Then again, Inter have the first option on him, so.
IMO, he's a perfect fit for Barcelona since he's an attacking LB with superb (from what I've seen) defensive skills for our style of play. Can't blame him for not looking good in the Serie A (at least, I don't think he's doing well there) when Italy can't have those types of SBs. Besides, attacking SBs thrive on possession. I think Nagatomo's price will skyrocket in a couple years.
I have no idea what we should do with the RB spot. Dani Alves can never be replaced. Not even Maicon will do (LOLOLOL). I mean, I believe the best replacement for that spot is Cha Du-Ri, but he's like 30 (I thought he was 22 in the WC X_X) and thus would be a short term replacement. Plus, he's not as good as Dani Alves. He won't be the full right side of the field and neither will Adriano. There's only one player that can do this and that's Dani Alves.
Hold on... LOLWUT Asians can play football? Believe it or not, they do, and if you watch them, Nagatomo and Cha Du-Ri are world class Barça-quality attacking SBs. And yeah, the Asian game requires attacking SBs, unlike Italy and England (to an extent). In the coming years, expect to see more Asian SBs play in the top leagues, which will mean less Brazilian SBs.
We need another CB when Milito leaves. In fact, we need 2. I don't want another Chiggy, Henrique, or Caceres (you know, young CBs expecting to break into the 1st team), so our scouts gonna scout. Abidal would be a more-than-sufficient backup if we get Nagatomo or another LB for next year.
CM is the big shady spot for the years to come. When Xavi gets old in like 1-3 years, we won't be the same. So it's either buy Cesc or cross our fingers with Thiago. And yeah, I don't know if any of the Asian CMs will cut it if you're going to flame me for joining the Asian bandwagon <_<
The wings are well covered, but we may need another striker as Villa is approaching 30 soon. I don't know if Bojan will cut it in this position. Seems to me that Pedro is more Villa-like than Bojan, too. Also, we can't sign a backup for Messi as there isn't anybody else in the world who will play like him.
But yeah, IMO, Nagatomo or another attacking LB must be the first option for next year.