My lineup would be (not just for tonight, but for many games coming in the next 2 months before Clasico,with the exception of Bravo playing in La Liga of course):
MATS
S.Roberto Pique Mascherano Alba
Raki Busquets Iniesta
Alves/Sandro Suarez Neymar
Let's give Alves a shot at RW, i think it could work really well, plus Roberto deserves 1st 11 right now more than any other player in the team, but at RB, not CM or even LB.
Like someone already said, don't break what is already fixed. As for full backs adapting to both RB and LB, you're forgetting one important fact, Sergi is primarily a midfielder, CM or CDM, so adapting to RB is already a huge acvievement and one of the few very positive surprises this season. Not to mention we have more players that can play in LB (Alba, Matheiu, Adriano and Vermaelen when they return). Right now RB is the bigger problem with Vidal not eligible and Alves in bad form again. Not to mention Roberto is fantastic on RB and should keep playing there, proving himself to Lucho and himself to gain even more confidence and hopefully becoming a legitimate first choice for that right flank even when Vidal does start playing. Trying him at LB would just risk all the progress he's making right now on RB, and he could be playing bad there, when infact we have like 4 other players that can play LB anyway, while at Rb we have exactly one more, and even he's in bad shape and form right now. To return to tonight, if Roberto deserves 1st lineup more than anyone else then on the other end it's Munir, who just doesn't deserve it with his egoism. So really hoping for him to be benched. And defence wouldn't be so exposed with Alves playing RW and not RB, because he wouldn't had to return so deep into defence, which we all know is the main issue when he's playing RB and then leaving too much space behind him on the right flank.
Some people are so funny, posting silly formations like 3-2-3-2 or something, thinking they're playing Fifa
I'm not saying it couldn't work, infact it could be interesting, but we all know Barca these last few years doesn't even try 3-4-3 anymore, much less some complicated Fifa shit, like some of you are describing.
Pep had 'balls' to try it on a regular basis, but then Tito and Tata just inherited that classical 4-3-3 formation and didn't try to change it one bit. At least Lucho is trying something new from time to time, but never so drastic as to play with 3-4-3 much less 3-2-3-2 or some other silly even more complicated formations.