Long time lurker, first time posting... Here's my appraisal of the situation and what I would do.
Goaltending: Perfect. Buffon is the best in Italy, and concensus Top 3 in the world. Mirante is a good young stopper with some upside.
No changes.
Defense: What strikes me watching this Juve club is how depleted the defense really is. To me, only Chiellini has what it takes to be a top 4 Serie A club starter. Zebina, Boumsong and Balzaretti seem the most capable of being substitutes and maybe Legrottaglie and Birindelli if they are in good form. Criscito and Grygera are good pick ups, but Criscito is still pretty unproven. Therefore, my priority would be on defenders. Two top defenders would be my top priority.
Desired Defense Lineup:
Chiellini-Barzagli-Luisao-Grygera
Subs: Balzaretti, Criscito, Boumsong, Legrottaglie, Piccolo
Cash in on: Zebina, Kovac
Midfield: Despite all the calls to blow the wad on a guy like Ribery, I think wings are one of three places where heavy reinforcement are not required. I'm a big fan of both Camoranesi and Marchionni, and with Brazzo coming in, I'd say that's set. Nedved is excellent there, but I think its time to put him back at centre midfield. Centre midfield has a gaping hole, as to me, only Zanetti is ready for prime time aside from Nedved, who is likely to switch between wing and CM. A world class hatchet man, like Gattuso would be nice, as would a Zidane type who can do it all and set up the offense. I think Almiron and Frings might be the best we can do there... for now, as I don't see Gerrard coming, though he'd be the best case scenario for Europe and Scudetto hopes.
Desired Midfield Lineup:
Marchionni-Frings-Nedved-Camoranesi
Subs: Salihamidzic, Almiron, Zanetti, Marchisio, Tacchinardi
Cash in on: Paro
Loan: De Ceglie
Forwards: Aside from goaltending, the most complete part of the team, as it faced the least cuts from the relegation scandal. Del Piero is all class, and if Trezeguet can return to form, they're set... for now. However, Juve needs to build for the future, and part of that is getting younger. I'd sell Trezeguet and buy Huntelaar... especially if he's as good as everyone says. Palladino looks to be a real talent for the future. I'd buy Bojinov's rights, but would loan him off, and perhaps sell him after next season for a profit, or bring him in full time. Zalayeta is the ideal depth forward, though he sounds unhappy according to some reports.
Desired Forward Lineup:
Del Piero-Huntelaar
Subs: Palladino, Bianchi, Zalayeta
Cash in on: Trezeguet, Miccoli
Loan: Bojinov
Ideal Starting 11:
Buffon
Chiellini-Barzagli-Luisao-Grygera
Marchionni-Frings-Nedved-Camoranesi
Del Piero-Huntelaar
Its a lot of new faces, but since the defense isn't exactly a strength, its a neccessary turnover.
(I probably missed some of the less remarkable loaned players)