While most people would benefit from a highly trained dog, that benefit alone doesn't mean they qualify as disabled under the ADA.
Whether or not a person qualifies is not something anyone here can address. It's a determination made based on careful consideration of the person's complete medical records and is best discussed with one's own doctor. Ultimately, the question is, "does your impairment substantially limit you in one or more major life activities?" Where "major life activities" are things like walking, breathing, seeing, hearing, thinking, etc.
My legs were crushed in a car wreck. I spent four months in a wheelchair and continue to use a cane. But I can walk. I can make it from the parking lot into a store, and nearly always can make it throughout the store under my own power. I can walk to the bus stop .1 mile from my home. I am not substantially limited in my ability to walk. A person who cannot walk 10 feet is substantially limited. Your doctor can help you determine which is the case in your situation.
You can apply for a service dog with a program and go through their evaluation to determine whether you qualify for their program. Here's an article that will help you find available programs:
http://servicedogcentral.org/content/node/262When it comes to owner-training, it isn't all rosy, and isn't the route most people should take in getting a service dog. Service dog training is far more advanced that pet training and requires considerable skill. Few people in the general public have this skill. Those that don't will face a very difficult learning curve, trying to learn while training the dog. The failure rate in these situations is very high. So you have to consider whether you are willing to risk owner-training, knowing that if your dog washes out you'll be back at square one, or take the program route which has a much higher success rate.
Here's an article on one person's experience with owner-training:
http://servicedogcentral.org/content/node/224If you do not already know how to train a dog to heel properly (ie maintain a position relative to your leg regardless of whether the dog is on leash and regardless of distraction and without deviation of more than 12 inches in any direction) then in all honesty, you aren't ready to train a service dog. The skills needed to train a proper heel are also needed for the rest of service dog training and a lacking in any one of those skills will result in an inferior dog.
Remember that studies have shown that of the general dog population, only one dog in a hundred really has what it takes to become a service dog. Without experience selecting and training advanced dogs, what are the odds of a person managing to pick that one dog. Also take into consideration that experts succeed within the general population at a rate of one dog in eight. That's why so many programs have gone to in house breeding programs to produce the dogs with the needed qualities.