All of the above, but I think periodic check-ins would get some engagement at the very least. Memes are fun and articles are informative, but unfortunately we're a bunch who's usually into whatever our hyper-focus du jour is, and it's not always going to be our ADHD. So I see those two as hit or miss, unless someone is dedicated.
But check-ins don't require forethought or planning (except for whoever starts the thread) and we can just pop into the thread to vent or laugh at ourselves or whatever.