I'd let KO go.
After that it gets tough.
They do need to get better offensively in that they need some cover for IT in terms of ability to get to basket. Brown will be there eventually but probably not next season.
So your core is IT, Horford, Brown.
Bradley's a tough call. Really good 2 way player who can play above his size. Can't create but gets hurt a lot. I'd probably lean towards keeping him.
Smart is the heart and soul of this team, also has a lot of value with the trend to small ball because he can guard above his size. But both he and the C's need to be reasonable.
Rozier is a lot like Smart and Bradley - his rebounding helps with small ball, better handle than both of them, better shooter than Smart, and he's still improving. But defensively he's still not Smart - not even close.
But the best players in this draft are guards. I think Danny's going to wind up doing something that none of us are expecting. They need a physical 4/5 who can pass/shoot/rebound. And Horford's age means you want to win right now.
Glad I'm not the GM.