My 2 cents.
Barcelona NEED a bare minimum of 3 signings. This is non negotiable. They have 3 glaring and imperative needs.
Absolute needs:
1- Starting Keeper. Barcelona absolutely needs a World Class starting keeper.
2- Starting CB. Barcelona absolutely needs 1 World Class starting CB.
3- Starting CM. Barcelona needs a World Class starting CM.
Then come the highly recommended borderline needs, but signings that are not absolute musts.
4- Second quality CB for depth. Highly recommended bordering on need.
5- Starting quality, preferably defensive RB, but ideally complete RB. Highly recommended, becomes a need if Alves is sold.
Then come the recommended, likely upgrades, but that are not necessarily imperative needs. Still, highly advisable purchases.
6- Scoring winger. Barcelona cannot continue to place all the scoring onus on Messi. They need wingers capable of manufacturing scoring.
7- Quality backup CDM. Barcelona cannot continue to count on Song to backup Busquets, simple Song is not good enough. Mascherano could be moved there, this is acceptable, though a better fit is preferred.
8- Mobile CF. Capable of integrating on the passing game, and also capable of being effective attacking from the wing throughout periods of the game.
Bench depth is also an important aspect to look at. Barcelona cannot continue to go on with their bench reinforcement being Song and Roberto. That is not good enough to win titles, I'm sorry.
My personal opinion is Barcelona should definitely sign the first 5 options. This is required to revitalize the club and give it the edge over others again. My opinion also is that the team should seriously consider and borderline require getting options 6-8. It is true to defense and midfield were the weakest links this season, but also the team struggled mightily to get scoring when it needed it most. They need forwards capable of scoring on their own, and they need forwards who threaten the goal to alleviate pressure from Messi.