Yeah, those all work great, and most of the significant activity hits one or the other.

I would add two more major ones among the biggest, busiest fannish communities on Dreamwidth:

fictional_fans is a general fandom community for new users and experienced ones.

fandomweekly hosts short fic challenges.

For an extensive (but probably incomplete) list of fanac on Dreamwidth, see:

Follow Friday: Fandom A-I

Follow Friday: Fandom J-Z

If you like having a list of communities per theme, with notes regarding their activity levels, then see my Follow Friday tag. I've been doing this since February, inspired by some discussions during snowflake_challenge in January, so there's a lot of coverage built up by now. I also link to those on followfriday, where other folks share their recommendations of various things too.