I'm a Y program director and personal trainer so I know just what you're getting yourself into. Go with all the Y has to offer - it's a lot and it's great - and prepare yourself. Personal training certification comes in many forms. ACE and NASM are the top two because they're very thorough but you can work as a PT anywhere in the country once you've got it. The other ones aren't recognized.
You can be an inspiration to others and I wish you well. PM me if you have any specific Qs.