Thank you everyone!
The filly I was looking at was an appaloosa. I've had appaloosa's before, and they've all had really patient forgiving dispositions. She has already sold, but I'm not discouraged. I've decided to wait until spring anyway. I don't really have the facilities to work with a young horse during the winter, and would want to be consistent; so I'd like to have the whole spring/summer/fall before winter so I could still comfortably work with the horse even with limited space.
But I feel so encouraged to do it. I think it will be a great learning experience to really see EXACTLY what goes into developing a good riding horse, not just what we do after they've been started w/t/c. I think we sometimes take for granted how well behaved our horses really are considering we speak human, they speak horse, and we're trying to meet somewhere in the middle.
I'll certainly start a training log once I start this project, with pics and info on the youngster. Wish me luck on finding the one! And any advice is still appreciated. If you have any ideas, methods, you want to share, let me know. I want to be 110% ready when I buy my youngster, so that I can give them a fair start, and blunder a whole lot less.