Need to give the Godfather offer for Cousins. A Horford/Cousins pairing would be deadly, and Horford would be the perfect character to put around Cousins to help him grow.
I'd offer Amir, Brown, Rozier, Young, 2017 Boston pick, and the 2018 Brooklyn pick to them for Cousins and Collison. That'd give them a really nice core to build around with Rozier, Brown, Skal, WCS and the high lottery picks they'll get the next two years.
We'd then have a championship-level roster with the following lineup:
PG: IT, Collisin
SG: Bradley, Smart, Hunter
SF: Crowder, Free Agent
PF: Horford, JJ, Guerschom
C: Cousins, KO, Mickey
That's a big lineup that will give both Cleveland and GS issues. Neither of those teams have someone that can stop Boogie down low. And hell with our spacing in that first unit, we could legitimately put everyone out at the three point line and let IT penetrate or Boogie work down low.