The questions should be fine for most people so long as they don’t go overboard with it. 2-3 should work. Select interests from a list (and have an option to fill some in), select moderation preferences from a list, and select a language/region from a list. There could even be a button that just selects an instance randomly for people who can’t be bothered (this can use the browser language to avoid sending people to instances in languages that they don’t speak).
Hot damn! Never thought that I’d see the day.