The 25 man roster looks pretty good as you state it, with the possible exception of Moncada, who is doing his best imitation of Ethelred the Unready, Barnes who has a good arm but is often ineffective and Holt who might be trade bait, although he is an effective utility guy, but he has trade value.
The 40 man roster you include Rutledge and Hernandez, either of which could replace Holt on the 25 man roster if Holt gets traded. Sandoval is that albatross that is hung around DD's neck. What to do with him? Marrero could be trade bait although a low value player. Holaday is only worth keeping as an insurance policy. Brentz is not that talented and outfielder or hitter and could be replaced with better. I don't know Romanski or Witte.
I would give a long look to Kopech if they can settle his motion down. A thrower like him might fit well into the BP, provided he has the right temperament for the team. I hear he is firey. At 21 next season, he should be old enough to make the jump.
Of the FA's, Ortiz is really retiring, Hill shouldn't be kept, Ziegler is good but he will be 38 and a big multiyear contract wouldn't make sense. Uehara is old and fragile and despite a good showing going out this year, we couldn't expect him to be available for much of the season. He is a no go for me. Tazawa has been good and if we don't wear him out he can be of value. Still good velocity, still a veteran who has good through the wars, and still young enough to warrant a contract, but not for huge bucks. Maybe DD makes an offer but can't land him.
Look to the minors before signing outside players.