Aloha Tatiana! I wish your questions had straightforward easy answers – and if you are government funded it kind of is. (See here: https://www.ada.gov/websites2_prnt.pdf) if you are not government funded, this is something that is currently being debated in the legal system. That being said, the WCAG 2.0 guidelines are a good set of guidelines to help protect yourself if you feel you should. (You can see more on WCAG here: https://www.yokoco.com/find-out-how-to-make-your-website-compliant/)
Just as you wouldn’t trust an overweight personal trainer or a skinny chef, you should probably never trust a designer with an ugly looking website or an SEO specialist who doesn’t rank well on Google or an “internet marketer” who uses direct outreach to generate leads. And by that I mean, if someone is selling you the idea of getting traffic through Google or Pay Per Click or Social Media, but they’re using cold outreach, like, they’re direct emailing you or they’re using word of mouth to get in contact with you, they’re really not practicing what they preach.
Tennessee v. Lane, 541 U.S. 509 (2004), was a case in the Supreme Court of the United States involving Congress's enforcement powers under section 5 of the Fourteenth Amendment. George Lane was unable to walk after a 1997 car accident in which he was accused of driving on the wrong side of the road. A woman was killed in the crash, and Lane faced misdemeanor charges of reckless driving. The suit was brought about because he was denied access to appear in criminal court because the courthouse had no elevator, even though the court was willing to carry him up the stairs and then willing to move the hearing to the first floor. He refused, citing he wanted to be treated as any other citizen, and was subsequently charged with failure to appear, after appearing at a previous hearing where he dragged himself up the stairs. The court ruled that Congress did have enough evidence that the disabled were being denied those fundamental rights that are protected by the Due Process clause of the Fourteenth Amendment and had the enforcement powers under section 5 of the Fourteenth Amendment. It further ruled that "reasonable accommodations" mandated by the ADA were not unduly burdensome and disproportionate to the harm.
Title II of the ADA prohibits discrimination against qualified individuals with disabilities in all programs, activities, and services of public entities. It applies to all state and local governments, their departments and agencies, and any other instrumentalities or special purpose districts of state or local governments. It clarifies the requirements of section 504 of the Rehabilitation Act of 1973, as amended, for public transportation systems that receive federal financial assistance, and extends coverage to all public entities that provide public transportation, whether or not they receive federal financial assistance. It establishes detailed standards for the operation of public transit systems, including commuter and intercity rail (e.g., AMTRAK).
Most recently, however, pizza chain Domino's has been brought under suit for their website not being accessible for specialty ordering. The U.S. Supreme Court refused to review the case, instead upholding the decision of the 9th U.S. Circuit Court of Appeals who said the “alleged inaccessibility of Domino’s website and app impedes access to the goods and services of its physical pizza franchises—which are places of public accommodation.”