Niche check part 2

This sounds crazy specific to me, but I think that means I’m on the right track.

I’d love to focus on women aged 20-35 working full time in a creative field (fine art, graphic design, illustration) who have 20-50 pounds to lose. Should I narrow this further down to just one part of the creative field (i.e. illustrators)? How do you know how narrow is too narrow? Thank you!