As someone who has been doing just this for over 13 years now, WOW, hadn't realised it was that long!
I can assure you that teaching the clueless is definitely not an easy option.
Like you I had always trained staff in my previous jobs. I always enjoyed that aspect of it.
I was asked if I would consider replacing someone who used to teach dressmaking at a shop. After various discussions and listening to friends, who had taken classes at night school, day school etc, complaining about them, I decided that the format of 'bring your pattern and fabric and make something' didn't really work. So I spent several weeks planning out a course covering various techniques.
If you have been training then you can teach, and you have a qualification in the C&G. After I had done mine I was tempted to do the teaching qualification but realised that I would be governed by rules and regulations if I taught in adult ed. and I had no desire to be constrained in that way. I'm not sure C&G is open to all ages now. They were changing it some years ago.
You need to think about what you want to teach and the level you will aim for. I teach beginners techniques but also have a group that now make clothes and get help and advice in the class. They have gone from complete novices to using knits, chiffon, making trousers, coats and being REALLY picky about the fit of their creations.
As already stated, you need to think about where you will teach, will you provide equipment etc, and insurance. my students bring their own machines. It is better if they are using something they are familiar with. If hiring somewhere the machines will need pat testing.
How many people you want to teach at any one time will depend on the type of class you run, time allowed and the space available. I have 6 at a time and that is enough. It can be a challenge to get round to sort everyone out sometimes. And beginners always have lots of questions and that takes up time that you may not allow for.
My tutor always used to say that you just had to be a week ahead of your students.
. I always make sure I have read through my notes, looked at my diagrams and have everything sorted before I start. It just makes you look better.