This is going to come across as blunt. But -
I think this is a very stupid idea. Getting an unbroken brumby, or an ottsb is going to end in tears.
As much as I were love it to be true, real horses are not like Flicka and the Black Stallion. You would have to be extraordinarily lucky to successfully break or retrain a horse as a novice yourself. In your first post you mentioned that you're maybe an intermediate rider at best, on *key word* a horse that you know and trust.
I don't think people realise just how much work goes into a young horse. Yes you may be good with them on the ground, be able to mouth them, get a saddle on etc. But when you're on their backs, they can be like slippery little worms. They have very little balance - it is the job of the rider to sit perfectly centred in the saddle, to help keep the horse balanced. If you lose balance on a breaker, the breaker then panics, you lose more balance, breaker bucks, you fall off, breaker learns to buck. Bad, BAD idea. You've then set the horse up poorly for the rest of its life and it resale value looks very poor. At this point you get the novice owners coming to forums like this, asking why their horse bucked them off or why they can't control them.
The absolute BEST move for yourself, right at this point, is to find yourself a nice quiet type that you can learn on. Get your confidence and experience up. Then ride some younger, greener horses for a while.
I purchased a warmblood weanling last year, having been around horses for many years, owned them since I was 10 years old, worked for dealers on nut case re-education jobs, taken ottbs, ridden breakers, competed extensively, and coached..... and you know what? I am terribly nervous about doing a poor job with my young horse. He is a wonderful little guy, his breeder gave him the very best start to life, he is super quiet and eager to learn, but I'll be sending him off for pre-breaking in the next few months as a 2 year old, and off to a professional breaker in his 3rd year for breaking.
Its just not worth starting a horse badly. Youngsters are like sponges, and what they learn in their breaking process will stay with them for life.
Not to mention, the likelihood of you getting injured in the process.