With Nimmo being a free agent I certainly hope Mets sign him but I think a Plan B for OF could be Joc Pedersonor or Adam Duvall. They could also pursue Trea Turner for 2B and move McNeil to outfield with Marte in CF and Canha in corner OF position. With Vogelbach back might be worth it to pursue a righty dh like maybe Brandon Drury.
Pitching-wise you want to sign deGrom but should he leave both Rodon and Tyler Anderson are reasonable fits as well as Seth Lugo who is a free agent. Bridge to Diaz in pen right now has Drew Smith would like them to re-sign both Ottavino and Lugo--Trevor May not so sure.
And depending on rotation, right now only Scherzer, Carrasco, Megill and Peterson in the fold--deGrom and Bassitt are my first choices but even if both return I would still add Rodon to provide depth and of course consider Taijuan Walker's return if it fits in the budget. I would like Megill and Peterson to be multi-faceted as they could be used as starters or relievers but to do that you need pitching depth.
As far as Alvarez is concerned, my hope is get him more time at AAA before making him either as DH and/or C