I personally could live with Calderon and Jackson.
My dream FA/Trade scenario is this:
Trade for Tobias Harris and put him at the 4. He is undersized but he rebounds well and is a try hard defender. Think David West with potential to stretch the court. If his rebounding improves, which it has with orl, and he becomes a better defender I see a young Paul Millsap. He has to improve his 3pt shooting though to help his efficieny. A another NY kid coming home. According to Brussard he gets a bump(shoe contract) for being in either Ny, Chi, or LA. That is a two horse considering CHi is stacked. Any, the reason I make the move during the season though is to make sure NY has the opportunity to match any offer sheet while also being able to go over cap to sign him, ala what Houston was going to do with Parsons.
If that trade is made I then go after Wes Matthews and Robin Lopez. Portland probably only has money for just one. They likely go with Lopez leaving Ny with a chance to grab a real two way SG(sorry Guns).
If the above is true then Gasol is probably my #1 center choice with Asik coming slightly in behind for different reasons.
If I have Calderon, Matthews, Melo, and Harris I would want Asik to be the rim protector and rebounder
If I have Jackson, Matthews, Melo, and Harris I would want Gasol posting and facilitating while playing good team and man D. Gasol is not a great rebounder but everyone else rebounds at a pretty high level for their position except for Matthews.
A starting 5 roster like those has just enough of right now and future if the knicks are able get Jackson and Harris. I do not see either one of them costing that much on the market due to their lack of extreme efficiency. They are both efficient enough to be starters with potential.