I think he has potential on the bases but it's much harder to teach routes and reading the ball off the bat which obviously is his biggest issue in the outfield. He doesn't need to steal bases (I feel like his first step might be a tad slow) but at the very least he should be able to become a valuable baserunner as long as he's always looking at his coaches.
You traded an elite closer for the opportunity to roster a 20 year old with no power in AA in a supposedly competitive year. I'd say woe is you indeed.
You must be new to relievers. They just...stop working sometimes. If he manages to stick in the league he could just as easily be an elite reliever next season, it's just how it goes.