Shooting becomes reliable once it becomes second nature.
Sorry for the long-winded novel above, but what I wanted to say about Mickey is that he'd be better for the rotation than David Lee who's putting up hollow stats. The sooner Mickey gets into the flow, the better. Zeller knows how to play Brad's style. He deserves rotation action.
13 guys can play? This is who I'd go with, in order of playing time:
PF/C
Amir
Olynyk/Sully
Zeller/Jordan
I'm not saying play all five. Amir will need rest.
Kelly, Jared & Zeller are the core.
Amir is a version of having KG in one of his final good years.
SF-PF
Crowder
Jerebko
Rotation Filler
Turner
RJ
Pencil these guys in for most of the guard minutes:
Avery
Thomas
Smart
That's 12 guys. I'd suit up Young or Rozier before David Lee for #13.
Maybe a team can be suckered into taking Sully and Lee. That would clean up the roster very nicely.
If someone wants Turner for a serviceable point guard, then with those few tweaks, we could win the title #18. We could be the rare champion without stars.
Stevens has that Butler mystique, though I don't think they ever won the national championship. I wouldn't underestimate the Cinderella factor working in the Celtics' favor in the playoffs.