Chances are he won't, because Ferdinand was an incredibly impressive footballer. I think the level of ability Stones has shown at a very young age means it's not an impossibility though. He had a very poor season last season, and this season has been mediocre, but it's very rare to see a starting 22 year old CB at any top club.
I can't disagree that Bravo has been very dodgy, but I think to some extent the differences for keepers between the PL and other leagues is overstated, I think the main problem has just been Bravo moving from a significantly stronger team to a weaker team with less protection. I'm not going to write him off though as it's still very early.
Agreed, Aguero is an incredible player and is their best/perhaps the league's best player. Saying that, if you took Costa from Chelsea, Sanchez from Arsenal, Ibra from United, Kane from Spurs etc, the team in question will lose points if their best striker is missing.
They rely on Aguero, but I think Silva, Gundogan, KDB, Sterling, Fernandinho, Otamendi have all been good to great this season. Iheanacho is also a very talented young player and good backup to Aguero.