OK, so now that we've got the 40 man set and Ohtani is cleared to come over, here is my dream 'rest of offseason' for NY:
Move Ellsbury to whoever will pay the most of his deal, 3/24 or 3/27, throw in guys like Mitchell and Cessa if you need to.
Move Castro's remaining 2/24 (plus a 2020 option), this seems possible. If Torres isn't ready out of spring training, it shouldn't be long after, and Wade/Torreyes can fill in any gap.
Resign Sabathia, ideally a one year deal but two if you really need to. He is (still) better than almost everyone seems to think, NY will almost certainly pay him considerably less than he would get if he was willing to sign anywhere.
Sign Ohtani (obviously every team is hoping for this to different degrees, but this is my dream).
Look into moving Betances if you can get someone to give up good value for his remaining two seasons, otherwise keep him for now.
Upgrade backup catcher to someone who is both better than Romine and who can tutor Sanchez defensively, maybe Alex Avila. NY can overpay some here if they need.
Then this is your team:
Rotation:
Severino
Tanaka
Ohtani
Gray
CC
(AAA depth: Montgomery, German, Adams, Sheffield, Abreu)
Bullpen:
Heller
Warren
Green
Betances (if not traded)
Kahnle
Robertson
Chapman
(AAA depth: Gallegos, Holder, Cody Carroll, maybe Acevedo or Loaisiga?)
No bullpen lefties except Chapman, you could force Shreve in there again but I don't think he's good enough.
Lineup:
Gardner LF
Judge RF
Bird 1B
Sanchez C
Gregorius SS
Hicks CF
Torres 2B
Headley 3B
Avila
Frazier
Andujar
Wade or Torreyes
Austin
(AAA depth: McKinney, Cave, Estrada, Wade or Torreyes, Higashioka)
DH can be covered in numerous ways here, Frazier, Andujar, Ohtani, plus half-rest days for Sanchez and Judge.
Gardner and Headley are on the last year of their deals, and their hopeful replacements would already be on the roster here in Frazier and Andujar, which would leave just Florial (bumping Hicks in CF) to fully complete NY's lineup makeover. Gardner has a $12.5M 2019 team option and will undoubtedly not go easily, good luck to him.