I don’t follow the 50 character rule, but to answer your first question: imo, no, don’t mention where you fixed the bug. This is a commit message that is explicitly tied to the place where you fixed the bug. You can go into more detail in the PR if you need to.
For me, it’s not great. The web interface and apps I’ve used are kind of bad, there isn’t a lot of content in the topics I’m interested in. I’m mainly here because I refuse to go back to Reddit.