The major issues for flick would be the fact that Barcelona themselves are almost entirely broke and for a club like Barcelona that wants to return to their former glory they would definitely need to bring in some players and that would require funds which at the moment seems to be some of their issues but even at that I still expect them to be different atleast they have some good players, it just all boils down to the fact that a good coach with good mentality needs to handle the club.
For me, the major problem for Barcelona next season would be quality squad depth. Barcelona is having some financial crisis, but they always find a way. Most people talk about them without really knowing the main issue, and of course, they don't care because that won't be interesting news to sell. Barcelona is still a very rich club, probably the second or third richest club in the world, the problems they're facing are not because they can't generate money, but due to the tight La Liga restrictions which don't allow them to spend as much as they earn.
Currently, Barcelona are facing the 1:4 rule. This rule allows them to only spend a quarter on whatever money they generate. This was put in place to help them pay off their debts and balance their finances. That was why it was difficult for them to sign players because even if they could pull off a big signing, they couldn't afford to pay them.
Now despite all these restrictions, Barcelona still find ways to get players of quality, like they've done in the past two seasons.
Currently, Barcelona is about to sign a deal with Nike that would take them back to 1:1 l. Meaning, they can spend as much as they make. This would make it easier for them to sign big players and pay them because aside from Real Madrid, no team in Europe generates more money than Barcelona.
Hence why I said the major problem Barcelona would face next season is squad depth. They're going to make signings this summer, but those signings would be to fill up the positions that need filling like the DM, LW and many 2 more positions. Flick is a player who works his players to their core and a manager like that needs squad depth to rotate his squad to avoid fatigue.
Four very quality signings and the right player sales would make Barcelona very competitive next season and I believe they know that.