The fact that you acknowledge that you do not know a whole lot about driving is a step in the right direction, Nancy!
It's those that think they know everything who are impossible in my book.
If you don't know how to ride, would you break your own Quarter Horse?
Training minis to drive isn't difficult if you have the foundation in riding and/or driving, but I know that I have made some pretty big mistakes teaching my horses to drive even after being involved with horses for almost ten years before I started driving. There is a lot that can go wrong very fast and if you don't have the experience to know what to expect, you can get yourself hurt or ruin your potential driving horse so that he will never drive. Been there, done that.
The problem with a lot of minis is that they are what is called "stoic", meaning that they "put up with" a lot, to the point that people mistake "tolerating" for "training". Again, been there, done that. Almost had a wreck with a mini because of it. If you can't tell the difference, you will end up with a horse that "pretends" to be trained, and you won't know until he blows up. There are A LOT of "trained" minis who fall under this category. Scary.
Also, because they are small, people have this false sense of security that they are "safer" than big horses. I just talked with a lady the other day that said, "Oh, come on, they aren't as hard as that big horse over there...." But I also have stories on my website of wrecks that people have had with driving horses, including minis.
I used to think that the owners were the best persons to train their horses because that is what I did and it worked, but I have also realized that the best trainers can "read" their horses, and that is something that is VERY difficult to train someone else to do.
At the very least, you can get lessons on how to work with your own horse to train it to drive. At least then you have an experienced person there to help you.
Myrna