I have a couple of questions you need to ask yourself:
Are you able to 'fix' spoiled horses and really bad problem horses? If you put yourself out there as a public trainer, that is what you are going to attract.
Can you put a pretty good 'finish' on a horse or are you looking for colts to start? There are about 100 colt starters for every person able to put a decent finish on a horse, either English or Western. There are even fewer trainers than can get one competitive or show ready. Which can you do or do you want to do?
If you want to be able to finish horses and get them show or event ready, your best bet would be to try to get on with a really good trainer as an assistant. Starting colts and warming up horses for a really well-respected trainer offers many more possibilities in this day and age than going out on your own right away. You will learn more, you will be exposed to a lot better horses and a there is a lot more future than the clientele any Craig's List ad will get you. Those ads will just get you hurt. You better have good insurance.
If you are only able to or want to start colts, why don't you just buy project horses, train them as far as you can and resell them. They are dirt cheap right now. If you can get a solid, 'gentle ready to ride for anybody' kind of horse made, you will make a lot more money and be able to do it YOUR WAY and make what you want. If you start selling these kinds of horses, I guarantee that you will have a lot of people want you to ride theirs -- so you can be 'picky' and turn away the spoiled crap if you do not want to deal with them.
JMHO and a few things to think about.