Roberts will be loaned out and Gundogan will be eased back in, possibly in the deepest role competing with Dinho/Yaya. So it's more likely 8 players competing for 5 positions.
Add to that Sterling and Sane will be rotated being young wingers. Jesus and Aguero will rotate. Plus we're not going to keep everyone injury free/suspension free.
Also not out of the realms to see something like this against weaker opposition:
-------------------------------Ederson
-----------Kompany---------Otamendi---------Mendy
B.Silva-----------D.Silva--------------Dinho-------------Sane
------------Sanchez----------Aguero-------------Jesus
Subs: Bravo, New CB, Sterling, KDB, Walker, Gundogan, Yaya
Plenty of flexibility with something like the above, allows you to get more attacking players onto the pitch. Could put Walker or Sterling where B.Silva is, could move Mendy to where Sane is and bring in the New CB. Could go completely mental and play Kev/B.Silva where Dinho is. Could drop one of the front 3 and play an extra centre mid.
I definitely think 3 at the back will be in Pep's thinking given the amount of attacking players we have/will have.
Two words. John Stones