I think Foden, Mount, Maddison and Grealish are all fighting for the same place and at the moment I'd say Maddison and Grealish are the best options. Long term I think Foden will establish himself as first choice.
That is pretty much what I would like to see as well, except at full back I think it's vital to have like for like replacements. I would prefer to use Foyth and Davies centrally and then bring in players to suit our style. Atal, Aarons, Grimaldo and Sessegnon for example.
With the players we have at the club, who look like they are part of the long term plans, 433 seems the best fit.
For me Ndombele is the key and I think we need to build a system to suit, which means a midfield 3 with a defined holding player. Lo Celso, Dele, Winks and Sissoko are also more...