I think Boston would have to trade Horford and a 1st to get Barnes and I wouldn't do that. Boston needs someone that can fit into the TPE or a guy that is a clear upgrade on a top 3 spot on the team, and Barnes isn't either of those things.
With Wood gone, I'd probably try to kick the tires on John Collins. Probably take Smart, but I think I'm ok with that.
Maybe something like this
Collins, Huerter
for
Smart, Grant, Nesmith, Theis, 23 1st
Main 8-player Rotation
PG - White, Pritchard
SG - Brown, Huerter
SF - Tatum
PF - Collins, Horford
C - Timelord
Use the TPE's and TMLE to add in depth and I think that is a better team with a better shot at a championship next year