Lopez is interesting defensively since he has played a bit all over. The bat is what the bat is. And I think they would have to make a 40 move to bring him north (which the Tigers have Turnbull to move to the 60 as a 40 move in their pocket). I suspect he's headed to Toledo, but who knows.
I think the roster you proposed seems a very reasonable guess. Lopez, Jimenez, Diaz, and Vest are probably up in the air, but we're talking the last position player and bullpen pieces that are probably lower leverage to start the season.
And I agree with you about Pineda's questionable availability out of camp. Off days are not exactly plentiful early on, so they will need that 5th SP. It's got to be Alexander, right? They can stretch him out right away and not worry about that. Who knows, maybe they go to 6 SP for a bit once Pineda returns.