Re: Robin or no Robin?
Im really not a fan of the Teen-Titans concept or giving Batman sidekicks (plural). A bat-family just won't work IMO. Dick, and then maybe referencing Jason's death is enough. Even just Dick growing up to be Nightwing.
I dont think we're getting more than 1 or 2 solo movies with Affleck in the cowl anyway. Probably one. So if they do prequels it'll be a different actor, and i dont think WB would do that for another 8 to 10 years.
Best thing to do, show Grayson in a scene in Batman vs Superman. Maybe the end of Justice League as well, when Bruce returns to the cave after the big mission. He gets rid of the drones, reconciles with Dick, and wants to be Batman in Gotham City again. Puts that old classic suit back on for the solo film. Keeps the high tech suit for the League outings.
Show Grayson helping out Batman, as Nightwing. But do some flashbacks to when Bats was in his prime fighting with Robin. Quickly show the origin flashback with Zucco, the circus, skip to when Dick is like 13 or 14 as Robin.