there are fist fulls of qualifications you can get, alot of coaches have a degree in some sort of sports science. there are then alot of varying coaching qualifications, CSCS, NSCA, UKSCA to mention a few. Some certs require case studies or exams and the thoroughness and requirements of which can vary alot.
Getting the certs and qualifications is the easy part. Getting the job is the hard part, the industry suffers from nepotism at the university level and sporting organisational level (you'll need a degree or Msc + cert to work at this level).
This is why alot of strength coaches start their own facilities and own services, the advantage in this is your qualifications really dont matter and sticking on a strength coach badge is easy so you really need to prove your self vs the rest.Ive had some great intern and work experiance but im still chasing that dream posistion.
if your curious i have a BSc in applied sports science and a Higher national diploma in the same, UKSCA, BWLA certs