I am planning to sell ebooks that teach productivity without using will power. I can niche this down in several different ways.

1/ Niche by targeting people who live in the Bay Area.
2/ Niche by targeting people who work in IT.
3/ Niche by targeting people who are 40+.
4/ Niche by targeting people with ADHD-Inattentive.
5/ Niche by targeting people who are INTP.

If I apply all the filters I might end up with a really small market. How should I choose which niche filters to apply?