First of all, if you are looking for the future, you need to think seriously about buying a horse bred for purpose. So, in the H/J world, this is a t-bred or WB, or possibly a 1/4/T-bred line.
Once you decide what general breeding you’re looking for, I would contact the breed association, and discuss what you are looking for, and get the local breeders in your area contact information.
Then I would spend LOTS of TIME going to their farms, talking to them, and checking out their stock. If something really catches your eye, even early on, and you are comfortable with the people you are dealing with, great! You can still continue to learn, and be comfortable with the knowledge that there is more than one horse that will be perfect for you. Do not feel pressured, but don’t get paralyzed either.
The more knowledgeable you are the more confident you will be in your buying decision.
Another piece of advice is this is a warmblood breed, if you really like a horse which is also a very good mover, if it doesn’t work for your purpose, it could be a very good dressage prospect or 3-day also. Nothing is cut in stone with horses. Most warmbloods are good at more than one discipline. Horses with great canters and walks for jumping, and that “sit” also can trot enough for dressage.
I personallly like to buy my horses as young as possible. Over the years horses which I have purchased older and under saddle have tended to have large “holes” in thier ground manners and experiences which has made the first couple of years under saddle more difficult than it ought to be. When you have your baby, you can spend the time with it, and build a great relationship with it from the get go, and the starting is a “non-event”. It’s really much better and incredible fun!
You also would not believe how many people breed and then “forget” to pick up feet, have the farrier visit, worm, vaccinate, and heck- even FEED their babies!! A horse you raise has excellent care- this means a LOT for future soundness.
When you start your own youngster, you are under no time pressure to put something together. If it takes him 3 months to figure out how to pick up the left lead canter, so what? You wait and giggle about it. A trainer has to produce the “picture” in 30 days- this is an awful lot of pressure that a baby really doesn’t need, and many horses do not do well mentally with this.
So, as a small breeder and very experienced young horse trainer, I highly encourage you to take the plunge. I think you will find the experience greatly rewarding.