The return for Ender/Teheran would have to be something along the lines of Soler, McKinney, Almora and Underwood plus one more piece. It would basically complete a total rebuild for the 2017/2018 teams.
I think I would rather build the package around McKinney too. He fits the timeline better for the Braves, and he doesn't have the same injury/bust potential as Soler.
McKinney/Contreras/Underwood would be a clear win for the Braves, so it's probably not realistic when dealing with the Cubs (or anyone that isn't the DBacks).
Something like McKinney/Almora would be pretty fair I think. McKinney is probably a top 50 guy now, so he has quite a bit of value. He seems like a young Markakis...very solid defense, but not fast enough for CF, fringe arm for RF, excellent LHed bat with average power.