Any recommendations for groups and subgroups in YNAB that give me a head start, without ending up with 100 groups?

you can start with my 100 groups and delete the ones that feel too specific that you won't be able to actually maintain them https://docs.google.com/spreadsheets/d/1l83_4ZfW5PBGkUsnPt7TJmgsx_JMZWTqf_ZInkHqH4Y/edit?gid=1830077275#gid=1830077275