I'll go by position. And some of these may not be realistic but I'm using Spotrac's free agent list so it should be current. And I wouldn't expect us to go after this many just listing who I'd like from positions available.
WR: Either or both of Keelan Cole and Will Fuller. We'll be losing Conley and Westbrook leaving just Chark, Viska, and Johnson. Mostly unproven and young. And cheap, we can spend some mid level bucks on a FA WR.
TE: Henry or Hollister, maybe even take a flier on a guy like Mo Alie Cox. Eifert won't be re-signed, neither with James O I don't think. Need more than just Oliver here.
S: Sorenson, Neal, maybe Hooker or Mills
QB: Fitzpatrick is the only free agent QB I'd mess with personally. If he signs somewhere else I'm keeping Minshew, keep the QB room cheap for a few years.
Free agent DL and LB are very dependent on what type of defense coach plans to run, without knowing I can't even speculate. But there are some intriguing names at rush backer if we switch to 34.
LT: Williams or Okung would be nice for a rookie QB to have.
CB I'd like to re-sign Sidney Jones. Otherwise Rhodes would be a great signing. Ronald Darby also had a good year.
Corey Linsley free agent C for Green Bay is interesting too. If we wanted to either move on from oft-injured Linder or maybe slide Linder to G and release Cann and/or Norwell.

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