I don't think Juve need a complete overhaul as mentioned by GDS. Core area of focus would be Sanchez as he would be the guy of all of the players rumoured that could actually help raise the overall quality of the starting 11. The other area would be a left back if we play with a back 4.
If it were me (and keep the costs down), I would do the following:
BUY:
Sanchez (22m)
Nani (8m?)
Adriano (0m on a bosman)
Peryra (50% of Isla + 6m)
Morata (loan with option to buy)
Gabbiadini (keep 50% and have him join us next season)
TOTAL: 36m
SELL:
Immobile (50% for ~10m)
De Ceglie or Peluso (2-3m)
Quagliarella (5m)
Vucinic (7-8m)
Osvaldo (loan expiry)
Sorensen (50% for 3m)
Padoin (2-3m)
NET: 6-7m
Squad:
GK: Bufon, Storari, Rubinho
DEF: Lichsteiner, Caceres, Barzagli, Bonucci, Chiellini, Ogbonna, Adriano, De Ceglie or Peluso
MID: Vidal, Pirlo, Pogba, Marchisio, Peryra, Asamoah, Nani, Pepe
FWD: Sanchez, Tevez, Llorente, Giovinco, Morata, Gabbiadini
The above squad is equipped to play 433 AND 352 with perhaps more depth for 352 with Adriano and Peryra (who can also play wing back).
Champions League Starting XI (4-3-3): Buffon, Lichsteiner, Barzagli, Chiellini, Adriano, Vidal, Pirlo, Pogba, Sanchez, Tevez, Nani. Bench: Storari, Caceres, Marchisio, Asamoah/Peryra, Llorente, Giovinco, Morata
Serie A Starting 11 (3-5-2): Buffon, Barzagli, Bonucci, Chiellini, Lichsteiner, Vidal, Pirlo, Pogba, Asamoah/Adriano, Sanchez, Tevez