Building Out My Personal Site vs. Building A Branded Site?

Long term, I want to build a product around email, and to get started I wanted to build a site that ranks on Google so that the product doesn't fall onto to deaf ears once it's built.

I can either build out a personal site and then once I figure out a good product to build in this space. Use the audience on my site to validate the idea and become my first user.

Another option would be to buy a domain now and build out the blog for that site prior to honing on exactly what email product to build.