One way you can approach this is to allow your niche to announce itself.

1) Start blogging.

2) Ensure your pages are SEO'ed correctly - mobile friendly + no HTML syntax errors + LD-JSON is correct + site's verified + sitemap is correct, your site runs latest LAMP + HTTP2/ALPN SSL, to name a few. Ensure all your onsite SEO is 100% correct.

3) Run small amounts of paid traffic to many of your pages. I suggest Outbrain for this.

4) Run Adsense on your pages.

The combo of #3 + #4 will likely create a profit stream or at least, neutralize... so your income pays for your traffic.

5) As your natural traffic increases, look at your Google Analytics to determine how people are searching to arrive at your pages.

Consider the most prevalent search criteria + formulate your niche from this data.

So in essence, let your readership tell you your niche.