Broad business Niche over haul.

Thank you for the feed back on my question “What to choose”. – so much clarity and direction from just a few words from you.
I am looking my target market : I teach people who want to start a business in Car or Boat upholstery. I am the only business offering these courses in my country so in one way I’m Niched but a very broad one.

The courses can be specifically niched ie:
– Established Campervan Convertors who outsource their work and want to take back lost profit.
– Classic car restorers on a long waiting list for upholstery and have no experience to complete work for themselves.
In all I can break it into 8 narrowed niches.

My question: is it ok to have this many or should I be dropping some of them? Should I target the specific niche markets rather than the broad Car and Boat audiences?
Im trying to liken it to SCS – Where Brooke has courses for different audiences but do they all start from the Self coaching platform or are they specifically targeted?