Courses & Membership site - Use a second domain or no?

Hey everyone. Long time lurker here. Looking for opinions. I have a personal blog website, which is my actual name. I talk about 3 different topics. Then I have a separate domain name with those exact 3 topics as the actual name of the domain. My goal is to sell courses and create a private membership website where people can access other content, a forum and what not. Would it be best to put it all on my "official blog" domain(The one with my name)..Or use the second domain as the membership and course website?

I have seen both done and not sure of the route to go here.

Thanks,

MI