`<a href="#start" role="button">Get started</a>`

Please, just use a link. This has a destination, so making it masquerade as a button gives so many false affordances.

Plenty of interfaces mimic a form process. If that's the case, and it's really just a page positional thing (not state), I see no problem making button-based navigation.

We don't scream and shout that page nav links all look like content links, after all. Well, maybe you do, but it's not 1996 any more.