For example, attorneys that meet with clients that are ill/injured and in wheelchairs.  

Although it has all bedrooms upstairs, it does have an electric chairlift on stairwell wall and has wheel chair ramps throughout the back yard.Section 8 in Austin does not pay any type of premium for these amenities so I'd rather not start there. 

This plan was for a perfect world, but last year I had a car accident in which I injured my spinal cord and left me in a wheelchair.

My question is, if I rent to someone in a wheelchair; is it my responsibility to add a ramp and lower the kitchen counter tops?

You will need to do some modifications to the house like adding bars, using lower tubs, wider doors, wheelchair ramps, parking,.......I know some investors who target patients with mental issues (rather than physical), since modifications to the house are less.

I was wondering if anyone in the Atlanta area can give me a contact for getting a house retrofitted for a wheelchair?

Assistance animals perform many disability-related functions, including but not limited to, guiding individuals who are blind or have low vision, alerting individuals who are deaf or hard of hearing to sounds, providing protection or rescue assistance, pulling a wheelchair, fetching items, alerting persons to impending seizures, or providing emotional support to persons with disabilities who have a disability-related need for such support.

These animals are to be considered no different than say a wheelchair or a cane.

., wheel chair, walker, etc., some states (if not all) will make you accommodate these individuals at THEIR expense, and then they are responsible for putting the rental unit back to the condition that  it was when they rented it. 

Just like a wheelchair, pair of glasses, live in nurse.