I run a smallish private forum (~4k MAU but pretty active). My philosophy for the real-time stuff is to update anything that can be updated without being distracting. On the thread list, the number of replies will update in real time but the threads won't move position (be bumped) until you refresh. Threads with at least 2 people reading them will have a subtle highlight that users can configure, this lets you know you have a decent chance someone will see your reply immediately; this fades in and out in real time too. New replies show up instantly inside of a thread (and so do edits and deletions). There's a real-time 'N users are currently viewing' counter for threads and the whole site at the bottom of the page but it doesn't tell you who is viewing it -- I think that's kind of a privacy violation and might discourage people from clicking around. I think the combination of these features lets users know the site is alive without feeling like a panopticon.