I think Barcelona still should make two transfers to specific areas. These areas are defensive midfield and centre-forward. Because in the defensive midfield there is still only Oriol Romeu. Of course players like de Jong and Kessie can also play there. However their main positions are central midfield so it is better to use them there.
For the other position there is only Lewandowski there. Barcelona don't need to spend so much money for bringing a striker. They can even loan someone who can be useful in Lewandowski's absence. Signing a backup striker should be even the priority for them.
Barcelona's current financial incapabilities has been the major reason why they've not been very active in the transfer market like they used to do in the past which might have an effect on the teams performance when the new season kicks off.
The club needs to sign few more players to their side especially getting another striker that'll serve as a back up to Robert Lewandowski in case of when injury, suspension or fatigue sets in