I host my own because it's cheap, less than 10 dollars per month, and I wanted to contribute to the growth of the Lemmy community.
Also turns out that it's another benefit to this: I don't have to get involved in the entire political debate of who federated with who. I just subscribe to communities I want anywhere.
Yep you need a domain name pointing to your instance when you run the installation of Lemmy and it will create a let's encrypt https cert for your site automatically.