Can Kessie fit in a 433, though?
If he plays as a Kante-like side DM, I think so, but I don't think he can play as a Van Bommel type 6 that sits at the base of that midfield V shape.
Kessie was at his best in that double-pivot, where his role was to protect the left side. Yes, when we pushed him forward as a CAM he could play bully-ball, but he also pressed there and Kessie does have a knack for scoring.
It looks like it is Ricci or Xhaka, not both. I think Jashari is coming in to learn from Modric, the kid looks versatile enough to play either regista-like or more advanced, I think he can do both. Javi Guerra looks like an RLC replacement to me.
Xhaka can play as the base of a midfield V shape, for sure, but with Ricci, he doesn't have the ball distribution that you'd want to see from someone in that role, that's my major concern. I think if Ricci is the choice, then someone like Kessie makes a lot of sense, you'll more-or-less replicate that Seedorf-Van Bommel-Gattuso sort of midfield--even if Ricci isn't a Van Bommel-type of player, but you'd base your creativity in Modric or Jashari, with your other two midfielders controlling territory and shielding your defense.
What Ricci does well, is maintain possession, at least that's what the most rosy scouting reports say. I am adamant that Allegri's philosophy with midfield possession is not to suffocate the other team and push into their half, but to pull the opponents into that trap to open space for surging runs from our attacking players--whether that's a full-back, winger, striker, etc.
I don't think Allegri is looking to replicate his last Juve stint--I have this suspicion that he wants to prove something with Milan, and taking over Milan without Europe makes that significantly easier. Based on the rumors we have, I think he wants to use power to overwhelm like he did at his first spells at Milan and Juve.