Agreed Angus, that pick is a good start to the rebuild.
Problem I see is that it's Cleveland. If it was GS, Miami, LA, Spurs (due to Pop), NY (if the FO can ever get its crap together) etc then they are place free agents want to go, Cleveland isn't a free agent haven.
Other hot destinations are Minnesota and Philly, and that's due to the roster, young talent and future.
The big ticket free agents in 2018-19 are Westbrook, Devin Booker, CP3, Paul George, Jabari Parker (if he returns from another ACL), KAT, Porzingis, Simmons and Boogie (most are team/player options). I can't see any of them signing for the Cavs without Lebron being there or the Cavs having to pay massive overs as they are going to struggle, even in a weak East.
Bagley or Porter Jr (in their first year) won't be enough to entice top tier FA's to the Cavs and there is no young talent waiting on the roster to step up and fill the void.
Potentially the Cavs could have one of the worst rosters in the 2018/19 season (hence tank mode for a few seasons and pull a Philly). The trade of Love is really important.
Just because you have cap space doesn't mean that its a good thing (trust me on that, I support Charlotte).