Most of those things came long before Reddit and still apply to just being online in general. Only the word "subreddit" is unique to Reddit, as well as certain in-jokes ("when does the narwhal bacon?"). Really thinking about it, I'm not sure Reddit was ever really unique at all. It just has a lot of users.
The narwal bacon meme itself was specifically reddit, as it was a deeply cringey joke post someone made as a shibollith to try to identify redditors in the real world.
It was the perfect mix of very awkward, very stupid, and weirdly preening that got people to "ironically" use it for a bit on reddit, which then spread wider.
Isn't it a lot harder to tell when people are just trolls? You have to look at multiple comments to see all the negative points they typically get to realize it's not with your time to respond to them
You can skip subs, flairs and the gamification aspect (trophys, medals, gold, ...)
Most people need to learn about communities and instances. Rest should be similar. OP, comment, post, DMs, ...
Etiquette varies. Some people here like people who are nice to each other. Of course this doesn't always work.
I also pay attention to upvote people who reply to me. And I keep shitposting to the dedicated communities.
The dynamics and technical details can be different in detail. Some things don't work as smooth (yet). And we're only a few people here compared to the big commercial platforms.
Comms = subs, though it'll take a while to catch on I guess.
OP is OP. Though even in Reddit it was somewhat interchangeable between the person who created the post, and the person who posted the top comment of whatever discussion is ongoing.
Edit etiquette should stay. Ninja edits are rude, unless you're fixing typos. Even edits made instantly after a post/comment can sometimes show up much later than the original post due to federation latency.
I do wish we had that three minute window reddit had where you cold fix typos or something without it appearing as edited. Happens to me so often but I usually jsut fix them.
That depends on your instance. Kbin gives that grace period, or at least when viewing from Kbin. It should be easy enough to implement, if the instance owner is willing.