A few things I'd change if it were my design would be:
1. Easier access to the bathroom. I wouldn't want people going through my office to get there.
2. Central location for the feed room and the tack room equals less steps for your boarders and for your staff to feed.
3. Since this barn is very long, more access in and out in case of fire. You only have two and one is narrow. I'd have three access points.
4. At least two access points for your indoor arena. One bigger one directly to the outside so you can bring in your tractor to drag the arena.