will Brad put Gordon on the bench or will Gordon have to volunteer for the role?
You don't bench your best player. Hayward is Boston's best player, he needs to be in the starting lineup. If you tinker with the starting lineup at all you either move Tatum or Brown to the bench (for Morris or Smart). Lesser players, but may very well be a better fit and would allow the younger guy more free reign leading the bench unit.
I actually think moving Brown to the bench would do him a lot of good and would also help Smart, so I'd start Irving, Smart, Hayward, Tatum, and Horford and let Brown have a bit more free reign and a more defined role where he can have the ball in his hand a bit more. Smart can then just be the defensive stopper and not worry about offense at all, which is what I think his role really should be (he tries to hard offensively on the 2nd unit).