When Montella took over Fiorentina, more than half (almost 2/3) of the squad was new. He knows how to start a new team by asking for the right players (although Fiorentina had a great DS which we don't even have).
Montella's style of play:
Obviously desires possession, fluid formations that change a lot during a season and sometimes games. No real fixed formation (depends on opposition and players in form).
Defense:
Usually sticks with 4 at the back, but equally comfortable with 3. In central defense, seems like only Romagnoli really fits with a possession based strategy. The rest of our CB's are not comfortable with the ball under pressure. I'd love to see Romagnoli on the left of a back three. Even if we stick with 4 most of the time, Montella usually spreads the CB's very wide in possession, dropping his DM in the hole and pushing his FB's very very wide and high (Cuadrado was deadly in this way). Abate and Antonelli (and DeS somewhat) are very good in WB positions, and especially Abate is quick enough to track back on turnovers. What this means is that our FB's will almost always occupy the opposition defense, making sure they don't defend narrow.
DM:
Must be very comfortable on the ball, able to slot into the hole in the center of the defense in possession, making long diagonal passes and shuffling the ball around the middle. Montella used Montolivo for this quite effectively. Will be great to see him back doing the same again, but he needs a deputy. Paredes seems a good fit, but if I had infinite money i'd get Javi Martinez.
CM:
This is usually a pair of excellent ball playing midfielders, able to run around taking up neat positions behind the midfield, maintaining possession and able to burst forward at any time. Borja Valero is extremely impressive in this role. I'm hoping that Bertolacci can redeem himself with this type of role that sort of fits his toolset. I don't see any other player fitting this role (i'd rather see Bonaventura higher up). Montella sometimes uses a defensive minded player, and Kucka might fit well there and is a good option to have against stronger teams.
Attack:
This pretty much depends on the players at his disposal. If he has wingers, he goes wide with a trident. If his team is stacked with AM's, he'll go Xmas tree or 3421 with two of them. Good central attackers and a quality trequartista? He goes 4312. He doesn't really seem to have any preference beyond maximizing the potential of his attackers.
For now, it seems like we're working to have a quality trident attack (we have no real wingers, maybe Bonaventura only fits) but we do have a good double pairing (Niang/Lapa, Bacca). We need a great AM. I'm guessing we'll get a right winger and a trequartista, to keep our options open. Montella is all about flexibility and he won't want to be fixed into one system.