You've gotten some VERY good advice and I ask you to please listen to it. As a new mini owner myself (not new to minis, mind you. I've been working with them for almost 5 years), I realize that it is crucial to heed the warnings and helpful advice given by those that know more than us.
Please, geld your mini. Stallions are rarely
well behaved, and when they are, it is because they have owners that have been working with horses for decades, not because they are naturally that way. We have two (a mini jack and a mini stallion) at our farm, and while we insist that they are well behaved, they are still not beginner friendly and I would NEVER let someone with only a year of experience with horses handle them. I didn't get to start handling them until last year, four years into my learning.
You must realize that color is not something that is always passed on, and there are actually more sorrel horses (I have one, actually) than any other color by comparision. It can be a beautiful color, but it is not something to let a horse keep it's man parts for ;) Not only that, but color does not win shows unless it is specifically a color show, and sorrels rarely if ever win those classes. It is temperment, conformation,
and bloodlines that do. And 99.99% of the time, it is the geldings that have the better temperment.
Is your little guy registered? If not, you won't be able to show him except for a tiny local shows.
Also, as far as therapy/driving goes, I urge you to get a professional trainer to help you break him to cart. Cart driving can be very dangerous (I've almost had one flip on me before) and if the horse gets spooked it is easy to be hurt or even killed. I had a trainer work along side of my to train my mare, Sour- so I got to HELP train her, but I didnt do it all by myself. I also took driving lessons for a year before starting to train Sour to be prepared. Driving lessons are expensive. PunksTank said not to start driving him until he's at least two, but I'd go even further and say don't start him until he's three. You can ground drive him and such, but don't hook him up until 3 and wait even longer before doing more than leisurely walks around the farm. My mare is 4 1/2 and just now starting to drive for more than 20-30 minutes at a time.
Lastly, therapy. The farm where I work is a Hippotherapy farm, and we use minis almost exclusively. However, we do not use them for riding, as they are not built to be ridden. We use shetlands for that. It takes a lot of desensatization and patience to train a horse for therapy, because they have to stand still and quiet while kids pull on their ears, shove fingers in their months, scream and thrash around them, and move around erratically. Our horses had to go through a tough 8 month training course to be ready to work with disabled kids. Not many horses can handle that and it takes a special animal for it. My mare, for example, is not the type that is good for therapy and never will be, no matter what. She is simply too impatient and reactive for a beginner or kid, let alone a disabled child. If your mini is not gelded at all, or not gelded before age two, he will never be allowed to be a therapy horse. It will be too dangerous. Once a mini learn stallion behaviors, even after he is gelded, he will remember them.
My mare and I
Minis are wonderful but are a big responsibility. Study up and take precautions! They're tons of fun once you know how to work with them safely.