The Department of Justice (DOJ) has specifically stated in rulings that websites should be designed so they are accessible to individuals who have vision, hearing, and physical disabilities. There’s a growing body of case law where the DOJ required companies to provide an ADA compliant website and levied hefty penalties when sites failed to measure up.

Because of this, among the greatest drivers of website accessibility are usability improvements and the reputation boost that it brings—or, alternatively, the lost business that organizations want to avoid as a result of inaccessible websites. According to a survey by the National Business Disability Council at the Viscardi Center, 91 percent of customers say that they’d prefer to shop at a website that prioritizes accessibility.
The debate over the Americans with Disabilities Act led some religious groups to take opposite positions.[32] The Association of Christian Schools International, opposed the ADA in its original form.[33] primarily because the ADA labeled religious institutions "public accommodations", and thus would have required churches to make costly structural changes to ensure access for all.[34] The cost argument advanced by ACSI and others prevailed in keeping religious institutions from being labeled as "public accommodations".[24]
State and local governments will often post documents on their websites using Portable Document Format (PDF). But PDF documents, or those in other image based formats, are often not accessible to blind people who use screen readers and people with low vision who use text enlargement programs or different color and font settings to read computer displays.

The 2014 case involving Peapod, an online grocery retailer emphasizes that being ADA compliant goes beyond your website. The settlement required Peapod to make its mobile applications accessible by March 2015 and its website accessible by September 2015. Since mobile apps are fast becoming the preferred method of online shopping, e-commerce sites must focus on app accessibility too. 
Your website is often the first thing your customers see when they’re searching for a business or service on the web. As the face of your organization, your website needs to be attractive and functional, offering the latest features that users now expect. To plan and design a site that both reflects your company’s mission and values and appeals to customers takes a professional web designer. While free online services can help people set up websites, web designers can provide a unique solution made specifically to meet customers’ personal or business needs.

This is the exact opposite of mistake #1. Let me start by revealing a dirty little secret when it comes to website design. Most people think, Oh, I’m going to hire a professional website firm because I want a “real website” As opposed to a Word Press website or something else. And what most people don't realize is that all websites are made from the same stuff.
ADA disabilities include both mental and physical medical conditions. A condition does not need to be severe or permanent to be a disability.[6] Equal Employment Opportunity Commission regulations provide a list of conditions that should easily be concluded to be disabilities: deafness, blindness, an intellectual disability (formerly termed mental retardation), partially or completely missing limbs or mobility impairments requiring the use of a wheelchair, autism, cancer, cerebral palsy, diabetes, epilepsy, Human Immunodeficiency Virus (HIV) infection, multiple sclerosis, muscular dystrophy, major depressive disorder, bipolar disorder, post-traumatic stress disorder, obsessive compulsive disorder, and schizophrenia.[7] Other mental or physical health conditions also may be disabilities, depending on what the individual's symptoms would be in the absence of "mitigating measures" (medication, therapy, assistive devices, or other means of restoring function), during an "active episode" of the condition (if the condition is episodic).[7]
If your hotel used responsive web design when creating your online marketing strategies, you’re already meeting many of the ADA compliant regulations for hotel websites. You will still need to make some changes, but you definitely have a head start. Making the changes now, before your business is the target of a lawsuit or government action, makes good business sense.   
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/)
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