I agree with mikeyp on the parameters he just laid out. I might make an exception for the Plekanec proposal, because I really like him as a player.
I'd say easy no to that. We don't need another 2C especially with term. Dubi and Wennberg are perfect for the top 6 C until PLD is ready and honestly I think he should start the year with us at 3C anyways with Hartsy to mold him like he did wennberg Dano and wild bill. The part that makes this an easy pass though is Milano. 0 reason to trade him when we get no upgrade in return. That's bad value to add him.
Plekanec has shorter term than Hartnell, the issue with Plekanec is salary. His total pay is as much as Hartnell is getting but in two years rather than three!
But in the unlikely event that ownership is fine spending the extra $, I'd do the deal (Hartnell + Campbell + Milano for Plekanec + Ghetto + 3rd). Ghetto and a 3rd is not quite enough for Milano, but it's close enough. And Plekanec is a better all around player than Hartnell. Similar production and age, but Plekanec is the much better defensive player. He slots the other centers into roles they can take advantage of. Of course, if the FO really expects Dubois to contribute right away then this wouldn't happen.