23 is the ideal number for me. 2 players in each position +1 versatile player.
Currently we have 23; however, Rafinha + Rakitic's future still to be decided.
I think 20 players + 2 GKs is more than enough IF players are good enough and EV will count on them. It's better to have a bit shorter squad so there are more possible opportunities for Barça B players like C.Perez, Fati and Puig (I still believe he should go on loan but looks like he prefers to stay at Barça B) than having Denis, Vermaelen or Malcom (I know most people here liked him but if he's not counted on by the coach then it's stupid to have him) in the first team.
Last season we had:
GK: MATS, JC
RB: Semedo, Roberto
CB: Pique, Lenglet, Umtiti, Vermaelen (+ Murillo and Todibo for 6 months)
LB: Alba
DM: Busi
CM: Raki, Arthur, Vidal, Alena, Rafinha, Denis (6 months)
RW: Messi, Malcom
ST: Suarez (Munir+KPB for 6 months)
LW: Cou, Dembele
So 21 players in total without counting mid-season loanees/signings (who didn't have much impact anyway) but some players are very injury prone (Vermaelen, Rafinha, Dembele) so we've had only 17 players who have played more than 1.000 total minutes in all competitions (Jasper was close as well with 990 minutes). On the other hand 7 players played 4.000+ minutes.
Now we have:
GK: MATS, Neto
RB: Semedo, Wague
CB: Pique, Lenglet, Umtiti, Todibo
LB: Alba, Firpo
DM: Busi, FDJ
CM: Roberto, Vidal, Arthur, Alena (Raki?)
LW: Dembele/Neymar*, C.Perez**
ST: Suarez/Griezmann
RW: Messi, Rafinha***
* I think only one of them will be at the club
** It's very likely Perez will stay in the first team for most of the season though he could still play some games for Barça B if/when all our forwards will be healthy
*** It seeems more and more likely that Rafinha will stay at the end which I'm not against (we should probably extend his contract for a season or two in that case though so he won't leave for free next year). I don't believe he'll stay fit for more than a few months but he has Valverde's confidence and will play when healthy.
So I would say we have a better depth than last season with 21-22 players who will (health permiting) more or less be counted on by Valverde though there are still some question marks about Todibo and Wague but I think EV likes both of them so they will get playing time over the next month and then it's up to them if they'll do good enough to earn more minutes.
I think our goal this season should be to reduce minutes of Suarez, Alba, Busi,... so no player (except MATS though I think with less CDR games Neto could also play some easier league games) would play more than 4.000 minutes. This should be doable with improved depth at their positions with the signings of Griezmann, Firpo and FDJ and moving Roberto back to midfield.
Messi ideally shouldn't play more than 3.600-3.800 minutes as well because with Griezmann and possibly Neymar (if healthy) we could start some games without him. I think it's a good sign EV didn't force him much last season after his injury and he didn't do this in the first two games this season either. I hope he wont' play against Osasuna on Saturday because with NT break coming he'll have almost a full month to recover and do a "mini pre-season" before his return.
I'm not sure if EV will trust Todibo enough to give Pique more rest (so he could again be overplayed but as long as he keeps form from the second half of last season this shouldn't be that much of a problem) but hopefully he will so we'll see if Todibo has any longterm future at the club or else CB will be among our priorities before next season.
Umtiti's injuries are concerning as well but I still trust him more to stay healthy than Vermaelen for example. Good thing here is Lenglet is very durable (let's hope [MENTION=21723]Pedro[/MENTION] I didn't jinx him) and good enough to stay a starter unless Umtiti will show he can stay healthy and return to (or close to) his pre-injury form. Which hopefully will happen because this would improve his market value and we could sell him next year (we'll need money if Neymar's deal will go through).