I looked at the eight playoff teams last year & noted how many starts were made by the #6 or lower starters.
I am quite happy Walt added a guy like Choo without giving up Leake. I know lots of folks here are not as high on him as I am but based on a stat like xFIP he rates as an average/above average pitcher. Nice guy to have as the first guy up when a starter goes down. Plus we don't know exactly how the team is going to use Chapman. I'd expect him to start or finish the year in the pen.
How would you handle the staff next year? I think I'd start Chapman in the rotation with a plan to move him to the pen after a certain innings limit is reached. That way he can build up his arm but also be available come playoff time.