Have you looked at WCAG?
$1​
I'm fairly new to web accessibility so not sure about the overall thoughts on WCAG, but I've heard it's the place to start.
​
Regarding pressing 'h' in NVDA, that's only going to take you to HTML elements of <hn blah blah blah\\> where 'n' is the header level.
​
The NVDA users guide has a good section on navigating web pages. press nvdakey+n, h to get to the user's guid.
​
Are you using something like react or angular to develop the app? I don't know how well those, or other similar frameworks generate accessible applications. If you are using some type of framework, hopefully they at least address accessibility in their documentation.
​
If you're going hard-core and writing all the HTML/CSS/Javascript by hand, my understanding is you want to use generic HTML5 tags whenever possible. customized components are often not accessible.
​
thanks for considering accessibility as part of your development. Hopefully it was also considered as part of the initial design phase, that's where it can be better integrated.