A few questions:
1) These 3 horses - did you improve their behaviour, or did it just not worry you? Having difficult horses is not a good indicator of how good a rider you are - it may just mean you're very confident and have a grippy seat...
2) Have you other horse experience other than these 3?
3) Do you have the money to call in professional help if you need it?
I have 2 ponies - one I bought as a 2 year old, backed and trained myself, who is now 9 years old, a bombproof hack alone and in company, schools nicely and jumps for fun. I'm very proud of how she's turned out. I took advice from as many people as I could, tried different things, enlisted the help of experts and instructors where necessary, and have a super pony at the end of it.
My second pony is now 1.5 years old and I got him at 8 months old. He's bombproof to lead out and about, easily caught, moves away from pressure (wherever it comes from), ties up, picks his feet up and holds them, is good for the vet and farrier, loads himself, has been to a show and behaved (mostly). I'm also very proud of him and intend to train him to be as good an allrounder as my mare.
I'm by no means a super horseperson, but I know what I want to achieve and work towards that every day. My key interest is to have horses that are safe and fun to be around, and that means no kicking, no biting, no barging, no bolting, no bucking and no rearing.
If you still think you can train a horse from scratch and want to try, why not phone around your local studs and dealers and see if they'll take you on and train you up - they'll get free help and you'll get experience. Good luck!