I read somewhere that Pep's favoured tactical approach in Germany against sides playing 4231 was to play with 3 at the back. Baring in mind how much of the PL plays a variation on 4231 then I'd suggest we'll play 3 at the back quite a bit.
Think it would suit Mangala too
I'm sure we will see 3 at the back eventually, but to begin with I think it will be bog-standard 433 and 4231 while Pep adapts the squad to his style of play and gets things working.
During the weekend he alluded to first building a team spirit and work ethic, and *then* moving on to tactics, and similarly at Bayern he didn't bring in the 3 at the back formations and more complicated, fluid tactics until the second season.