Regarding the 9mm, I believe that is to differentiate it from the newer through axles seen on MTBs now. Virtually all modern bikes (without through axles) use 9mm axles, so you have nothing to worry about. Your QR skewer should have plenty of threads.

+1 I would look for something a bit shorter if possible. A smaller ATC will make the handling a bit "quicker" and probably liven up the bike nicely. Otherwise, I wouldn't consider it a deal breaker.