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.