I think the least talented of those 4 is Palladino, yet he is already playing himself into the team. Those other 3 will surpass (in their respective position that is) Palladino, I think. Hence, i'd be reluctant to let any of them go.
I like all of our youngsters, and rarely you can get a good value for these budding stars, even if you take into consideration their risk factor. But if we are to get Barza, they will be the key to facilitating the deal, since Palermo is a team that is looking to move forward, not simply cashing in their prized assets. Hence, I say let Milan have Barza, and we should try to buy Heinze or Metzelder for free. Obviously, we are going to face tough competition regarding these players, but unless Barca, Milan, Inter or Real jumps in, I don't see many more attractive offers than Juve in Serie A. More importantly, we can guarantee these players a first team place in a top competition, and in a top team. I like our chances landing one of them. And sign Jacques Faty for free to pep up the depth in the defence.
Grygera, Metzelder/Heinze, Kovac, Chiellini; Biri, Balza, Faty, Cristico, Legro, Wingback doesnt seem too bad IMO. Not as good as Inter, Roma, or Milan (When fully fit), but other than that we should have the best defence. And Buffon could the real difference maker. With Buffon as a Porteri, we are almost on part with Inter, Milan and Roma; simply because our GK is so much superior to others.