Technically once you accept any kind of renumeration for riding, training, or coaching, you are considered a professional and must show in open and pro classes, regardless of your level of riding/showing experience/etc. Now depending on what discipline and where you show, this can either work for or against you. For smaller and local shows, you may find that the open and pro classes are very small, compared to the amateur divisions. Or if you are competing on national circuits, this is where you may to find yourself in a larger class with many big name riders.
So it just depends what you want to do. If you plan on doing shows later on where you really would want to keep your ammy status, then I would hold off.
I know you didn't ask for opinions directly on the CHA course, but in my experience it's not the most helpful certification you can have. It's so easy and accessible for just about anyone to get, so it's not held in very high regard. Just about anyone could take the "clinic" and then call themselves and instructor. Better than nothing I guess, but probably not going to help much if you are planning to get a job instructing at a larger barn or want to do more and progress later on. I personally would do lots of research before doing anything, to find what would be the best for you in your situation.