This might be a bit long but I know a two women who have just finished their personal training certificates and I've used personal trainers regularly for over 2 years now so I have some experience of it.
I know the training courses differ in quality and price - that won't matter to most clients but it will to some. This is discussed on online forums so its easy for clients to check the quality of training and I've done it myself. Also, just a warning about stuff you have online - one newly qualified trainer i know put loads of stuff on her twitter account about her training and how crap her training course was - not a great idea when starting a new career 
I would now look for a personal trainer that does some sport themselves regularly - running, triathlon, cycling, weight training etc, or has a previous qualification in some kind of physical arena (like an ex army PT, sports coach, physio). i personally think the qualification is the starting point and you need to keep up to date with all the latest physiological research etc and how this applies to exercise. My current trainer has completely rehabilitated a shoulder injury i got from a cycling accident 18 months ago - (3 months ago i was looking at surgery). He was confident enough to build sometimes painful exercises into my programme based on his knowledge of weight training and how the shoulder works. My previous trainer was crap at this and had no idea.
You'll have a selling point in that you will have things in common with lots of gym clients in that you have reached your own goals first, you have a family etc etc. I think we certainly need more female PTs over the age of 25 as all the ones at my gym are male and I think there is a big market of female clients who don't want to work or aren't confident enough to work with 25-30 year old males. There is also a market in rehabilitation PT (level 4 i think) for people with health conditions - i think this market will grow in future as people want to stay active longer.
Also, getting off the ground might be difficult as you won't have any client testimonials. However, if you look good, and are seen working on yourself in the gym and getting results then I would approach you for training (this is how i chose my last trainer)
Good luck - I love my PT (not literally) and its one of the highlights of my week 