I love this. I also built a business like that[0]. It's super niche. I have maintained this small business for soon to be 13 years now. Most of what has worked has been maintaining great relationships with the few customers I have. I think the most important thing for me have been offering amazing support. I always reply to all e-mails right away and make it my top priority giving them my best help.

Congratulations on your success, and best of luck going forward!

[0] https://www.mino.no.