The Bills need to find a run-stuffing DT in FA. That is ONE single move they can make to improve themselves immensely on defense. Getting Spike back will be important, and there's a chance to improve by replacing Posey. As for DB's, Clements is franchised and either stays or gets traded for a 1st, which the Bills use on a draft pick.
On offense they do whatever it takes to get a good O-line. They have some pieces in place it seems with Peters (at LT), Gandy (at LG) and Preston (at OC or RG). If Moulds takes a paycut and stays, great. If not, the $5.5M goes towards getting a Wayne or Givens to replace him.
They have a ton of cap room, good draft picks and an extra draft pick or 3 (depending on comps), and hopefully a decent GM is coming.