Only realistic FA signing that I like is bringing back Costanzo. Going to skip the obvious NOs (the head case Freeman and DHB) and go straight to your mock:
I like Beckham, I really do, but it would be a pretty big reach trading up for a WR that is projected to go in the early-mid second round. If we want Beckham, it would be more logical to trade down and pick up a higher pick in the second to get him.
Always shake my head when I see mocks having us take a DE/DL early. Jeffcoat would be depth that barely sees the field next year. Same story with Gabe. We got away with shoring up depth picks last year but I'd much rather pick up players that can make instant impact to our secondary and possibly C.
Sam Shields would be too expensive; you have us losing two CBs but replace them with a rookie CB that has poor man coverage skills/technique and another CB that will be on IR the entire season (love the Colvin pick but would rather take at least two difference making CBs ahead of him that will be ready at the start of the season). That's not improving an already average (at best) secondary.
I like the Trey Millard and Martavis Bryant picks but the rest is pretty disappointing and I'd be underwhelmed if this happened. As posted above, all the ammo and not enough difference makers.
Overall, I don't see how these moves make our team better. And if we want to win the Super Bowl next year we need to be better.