as your colt gets older are you not concerned he will breed his mother? Or the stallion may see him as competition and try and kill him?
Also, are you aware of the fact that it costs way more to raise a foal from birth than it does to buy one that is green broke to ride. Plus you can pick out exactly what you want. What if the mare has another colt? Are you just going to keep allowing her to be bred?
Based on your posts it's pretty obvious that you aren't very experienced with horses. What do you know about training young horses? Or handling stallions? How about conformation? How do you know you aren't breeding horses with bad legs that are going to have all kinds of medical issues in the future, that will cost you thousands?
I'm assuming you have no plans to geld the colt? The colt will be old enough to breed before you know it and he WILL breed to his mother. He will also breed to his sister (if the mare does have a FILLY).... That is, if the full grown stud doesn't kill him first.
You may think this is all a good idea now, and that you've got it all handled. But I GUARANTEE, if you don't change your tune you are going to have some serious problems on your hands, and there will be 4 more horses on this earth that aren't being handled or cared for properly, to add to the thousands that already exist.
I'm serious when I say you are playing with fire, so don't be surprised when you burn yourself bad.
This is just sad.