I think he's a good fit in the backcourt with Smart, and I see no reason why he couldn't start.
On offense: IT the primary ball handler, good initiating the pick and roll. Smart struggles in the pick and roll but good spot up shooter from distance.
On defense: Smart big and strong enough to cover shooting guards. Let Smart take the bigger or more dangerous of the backcourt assignments when he's on the floor with IT.
As for a second unit, I would agree that playing IT with Bradley would be too small and would risk being eaten alive on defense. However, you could pair Bradley with Turner, and let Turner handle the ball and Bradley play off the ball on offense, while letting Turner take the bigger of the defensive backcourt assignments.
In total, a good fit. And if IT proves to be just a scoring spark plug off the bench... fine, he's making pretty modest money by current nba standards.