I let an ACSM certification lapse over 25 years ago. To me the exercise physiology questions are tough. I didn't go the NSCA route, I'm not interested in football and or olympic lifting. I checked out the test and It didn't seem so daunting. I went the NASM corrective exercise route as most people are dysfunctional and I think its emphasis on stabilization is perfect for what runners need.
If I were starting out today I'd do an internship with Cressey, Robertson, Boyle or Exos.
Joe Kenn and Mike Robertson might be developing their own certification I'd get theirs or Boyle's.
The ability to coach, to give proper cues, correct mistakes and give the right progressions at the right time is what any coach needs. Some Cross fit coaches are great, some are quacks, the same with running coaches.