Yeah, Valverde is a good appointment. Also, wasn't he a Barcelona player?
A safe if not inspirational appointment. He should be able to bring a bit more organisation and defensive solidity to the side. A 'competently' coached Barca, should obviously be up there with the best. They haven't been coached well this season, and even then they got to the CL QF's and ran Real relatively close. And I think Valverde is an upgrade on Enrique.
They are for the first time in a while in major need of reinforcements though. At a minimum, they need a RB, CM and RW. Ideally, an additional CB to compete with Pique and Umtiti (who was their only good buy last season)
Valverde usually plays 4-2-3-1. If he uses that formation at Barca, expect Messi to play in the middle of the three, probably his best position now, but they'll need a top class player for the right of the three, and ideally someone energetic, physical and a good passer to play alongside Busquets - ala Toure in his prime. They want Veratti, but that won't happen.
----------------------Ter Stegen/Cillesen
RB/Vidal-------Pique/Marlon-------Umtiti/CB-------Alba/Digne
-----------CM/Roberto/Rakitic-----Busquets/DM
RW/Vidal-----------Messi/Iniesta/Alena-------Neymar/Deleufou
--------------------------Suarez/Paco
RB's they've been linked with/potential options: Semedo, Cancelo, Azpilicueta, Bellerin
CB's they've been linked with/potential options: Sanchez, Lemos, Upamecano, Marquinhos
CM's they've been linked with/potential options: Keita, Fabinho, Veratti, Raibot, Seri
RW's they've been linked with/potential options: Cancelo, Dembele,
I don't think they'll get anyone from PSG. Their interest in both Marquinhos, Veratti and previously Thiago Silva has been long known, but PSG won't entertain any offers. I think Davinson Sanchez would be a good understudy as the third CB option and understudy to Pique. Marlon from their academy would be a 4th option. Would mean they have three young/relatively inexperienced CB's though.
Out of those linked at RB, I think Semedo would be the best option.
CM is tough. They won't get Veratti, and given the way Barca play, few fit their profile. I think Fabinho would give them good balance, but I don't know if they've shown much interest in him.
RW is even tougher. I think they'll get Dembele at some point, but not quite yet. And I can't think of many RW's out there who could come in and be a genuine good fit. They'd probably want a left footer for balance, or at least someone ambidextrous (Pedro, Dembele type) but I'm struggling to think of anyone who is available.
I think Mascherano, Turan, Mathieu will leave. I think there is a chance that Gomes will as well.
I think Rakitic, Roberto, Paco, Alena, Marlon, Iniesta, Vidal, Deleufou, will be in and around the squad as options.