What is a history of people with disabilities, including major events that have affected them as a group? US Supreme Court Cases? Major cultural traditions or background? Current demographic information?

In terms of selecting a specific disability for which to trace the history, it is important to realize that some disabilities were identified much earlier than others; for those, there will have a tremendous amount of published information to consult. Those that affect large numbers of people in the United States, such as blindness and deafness, have been supported by an increasing number of organizations since the nineteenth century. It is estimated that there over 7 million blind adults and about 700,000 blind children in the United States. To begin conducting research on the rights of Blind and Deaf people, respectively, you might begin by consulting the website of the National Federation of the Blind (https://nfb.org/) and National Association for the Deaf (https://www.nad.org/).
Any specific disability is generally distributed across people of all cultural and racial backgrounds, although percentages (actual and reported) vary. One notable exception is military veterans, who are more likely to sustain disabling injuries than the general population (https://www.dav.org/get-help/). Overcoming preconceptions about the relationship of disability to a particular background has been a significant feature of civil rights and human rights activism for people affected by HIV/AIDS (https://www.hiv.gov/hiv-basics/living-well-with-hiv/your-legal-rights/civil-rights).
In the United States, the rights of people with a number of disabilities are guaranteed, at least nominally, under the Americans with Disabilities Act (ADA) of 1990. The ADA has four key areas: employment, state and local government, public accommodations and commercial facilities, and education. Legal challenges have taken on discriminatory practices in all of these areas since the passage of ADA. The US Courts website maintains statistics on the numbers of cases.
While many claims are filed at the state level, a select number may be heard each year by the US Supreme Court. One notable case decided by the US Supreme Court was Bragdon v. Abbott (524 U.S. 624) of 1998, the first case the Court decided concerning the rights of persons with HIV/AIDS, in a case involving dental procedures.
https://www.glad.org/cases/bragdon-v-abbott/

https://www.uscourts.gov/news/2018/07/12/just-facts-americans-disabilities-act