If you need to adapt a car for disabled use, the first thing to consider is the type of car itself and the nature of the disability. Someone without the use of his or her legs, for example, probably doesn't want to buy a truck or van because the seat height won't allow them to transfer from a wheelchair to the seat based on the difference in height. There are many other disabilities, of course, but that seems to be the most common one that is addressed when it comes to people getting a car for their disability. No matter what the disability, though, being able to get into and out of the vehicle is the most important issue and the main thing to consider. Once you've found vehicles that are accommodating in that way, it's time to see how they can be adjusted so that they will work properly for a handicapped person. Both of these issues must work together - a vehicle that can't be accommodated properly won't work, but what type of accommodations can be made at all (no matter what kind of vehicle) also matters. Some disabled people will simply not be able to operate a specific kind of car.
Also, it's not realistic to only assume that getting in and out of the vehicle and operating the brakes, gas, and steering are the only things that matter. Mirrors might have to be adapted, and safety belts may need modification, too. The same is true for the seat and the wheel as well as any other controls that work things like the radio and the air conditioning. Talking to people who have adapted vehicles for a disabled person as well as checking with companies that routinely do that sort of thing can be a great help when it comes to whether the vehicle you're considering can be adjusted and adapted to work the right way. You can get lifts that can lift you from a wheelchair and place you into a car, and you can get lifts that place you and your chair into a vehicle. Dealing with a disability can be very difficult, but that doesn't mean that you shouldn't work at doing all that you're capable of. If that can include driving there's no reason why you shouldn't investigate adapting a vehicle for your needs and usage.