The Buffalo Bills are one of those teams that, on paper, I think should be successful. Maybe I'm just blinded by their hot 5-2 start to the last season, but I feel like if you got a good DM, a Monster Manual, four nerds, and a well-drawn map you could D&D the crap out of this team and come up with a playoff berth.
In actuality, they have some problems. Is Ryan Fitzpatrick the man, for example? Will they actually go a whole season without sacking an opposing QB once? How old is Stevie Johnson, actually, because the dude acts like he is twelve.
Save the Fitzpatrick question, I think these other two questions will be answered in FA - or at least addressed.
In regards to the pass rush, the Bills may not be super aggressive in FA since they have a top ten draft pick this year and some good pass rushers abound. That being said, if they target a guy on draft day at, say, OLB then it is plausible that they may try to find a DE through FA. Regardless of their overall approach, they really need to make some move on this front.
What to do about Johnson? He is an unrestricted FA this year and will probably test the waters. While not a top tier guy (at least in my humble opinion), he could field some pretty nice offers from some team who won't care about his antics.
If they want to keep him around (probably with a Franchise Tag), do the Bills go look for more WRs? They are pretty monetarily committed to Fitzpatrick, so getting another target might not hurt. Like half of their FAs are WRs too, so it might be smart to start signing somebody.
When all is said and done, though, the Bills have like Scrooge McDuck amounts of money in cap space, somewhere around $30-35 Million (source). Whether or not they will fill the space is up to them (duh), but should they want to make some serious moves, the totally can.
Unrestricted Free Agents: RB Tashard Choice, WR Derek Hagan, WR Steve Johnson, WR Ruvell Martin, WR Roscoe Parrish, TE Scott Chandler, OT Demetrius Bell, LB Andra Davis, LB Kirk Morrison, LB Reggie Torbor, CB Reggie Corner, S Bryan Scott, K Dave Rayner.