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/)
Since March 15, 2012, ADA compliance with the 2010 Standards will be required for new construction and alterations. In the period between September 15, 2010 and March 15, 2012, covered entities may choose between the 1991 Standards ADA Compliance (without the elevator exemption for Title II facilities), the Uniform Federal Accessibility Standards (Title II facilities only), and the 2010 Standards ADA Compliance.
Navigable: Content that’s repeated on multiple pages can be easily skipped. All pages have informative titles, headings, and labels that describe the page’s content and hierarchy. Navigating the page must take place sequentially, in a meaningful order that preserves relationships on the page. All link text is descriptive in order to make clear where the link will take users. If users are navigating via a keyboard, the current focus of the keyboard is always highlighted and visible.
Talk to your web designer about other techniques that will make your site more user-friendly for people with disabilities. Worried that’s not in your budget? Consider the fact that DOJ fines start at $75,000. And it's still yet to be determined if a non-compliant website is liable for one fine or will be charge per page for each violation. As the recent lawsuits illustrate, though, settlements quickly add up into the millions.