Be respectable
This should be the bare minimum. The Detroit Tigers can't be an embarrassment again. Fan apathy is already at an all-time high. Being laughably bad again would cause any fans that are still bought in to check out.
By respectable, I don't necessarily mean contend, though that would sure be nice. I'm talking what happened in 2021, when the Tigers exceeded expectations en route to a 77-85 record. There wasn't a ton of talent on that team, yet they were still fun to watch for a few stretches. I think many people, myself included, would settle for that at this point.
Re-entering the "bad, but fun" phase of this rebuild would be the least this team could do. They have more talent than the 2021 team did. That team didn't have Riley Greene, Spencer Torkelson, Austin Meadows, or Javy Baez.
Combine this with the aforementioned new coaching staff, and there's no reason why this team can't be respectable. The fans can't take much more bad baseball.