I'd be fine with Trae, but I wouldn't trade Brown for him. I don't like that value enough.
That said, I had proposed something like this before and I still think it makes a lot of sense for all 3 teams
Boston - Lillard, Collins, Little
Atlanta - Smart, Brown, Kornet
Portland - Young, Gallinari, Pritchard
Other players and draft picks could be included.
The Blazers get a young star signed long term to be the new face of the franchise. He will sell tickets and put butts in the seat and he has led the Hawks to the playoffs (including the ECF). The Hawks get out of the Young headache and fit for a local star that should fit better with Murray. And the Celtics get their closer and more big depth.
Boston post trade
Starters - Lillard, White, Tatum, Collins, Rob
Main Bench - Brogdon, Hauser, Little, Grant, Muscala, Horford
Deep Bench - Davison, Champagnie, #35
Still 1 open roster spot and that assumes all 3 deep bench make the actual roster and 2 aren't the 2-way players.