This is NOT about joining an Instance on Mastodon I.E. setting up your account, as you might at Dead Bird or Facebook. This is about setting up an actual Instance over there. (If you don't know what an instance is yet, you have some work to do.) There are all sorts of laws, worldwide, about liability and running servers on the Internet.
As a co-founder of Dreamwidth, this person is one of the few who can speak on this topic with a lot of knowledge. But when she tossed this up, she didn't CUT it, and it's a monster post. So here's the link, if this topic interests you.
I am all about Risk Management, which is one of the reasons I am still here. And thinking about closing my own web site and just doing essays on Dreamwidth.