Lots of good info so far. And I agree, loving to workout yourself isn’t the best foundation for a successful and/or long-term career as a trainer. That’d be a bit like, “I like taking vitamins and being healthy, so I’ll become a doctor.”
Some good reading about the profession, from Alwyn Cosgrove:
And here’s what I, quite biasedly, consider one of the single best threads on this forum.