Depending on growth and projection, I'm not too worried about WR. Moore needs to learn how to catch, the other two have to learn to run better routes. In theory at least, both problems are correctable.
I don't like saying, "We have to sign this guy" or "that guy." We don't know who'll even make it to free agency. And the usual problem is the really great players, the impact players, are expensive. Getting one might be it. Two would be surprising and three would be outright shocking.
That said, the holes on the roster are pretty obvious. Edge and R G/T are the top, Safety and TE the next tier.
McCray/Bell haven't done well, Bulaga is getting old and hurt too often. I'd expect something like the usual--a couple of college LTs in the 4th/5th that can't hack it at LT in the pros. Generally a good way to get pass protectors. Maybe slide Bulaga inside depending on what we can snag. Doesn't help him get injured less, but might let him be successful long with (what I assume) is a slowly declining athletic skillset. Seems unlikely we sign anyone other than a Bell-like signing.
Matthews is an FA, Perry has been hurt. I think we can all agree on this one, no arguments here. I wouldn't be surprised if we re-signed Matthews to an incentive laidened deal. I dunno, 3-5 million base, ability to earn around 8-10 depending on those incentives. Let him be the number 3 OLB. Signing and Edge is going to be the hardest due to the premium the league places on the position. Maybe a value signing, ala Peppers.
Safety needs help, but scarily enough, we don't seem to be losing because of it. I wouldn't be surprised if this is the big splash signing, because across the league, Safety salaries are overall down.