You'll see this on the re-read, but Ms. Wong will be accompanying the Avatar and the Anti-Comet taskforce as an embedded reporter.

>Who's watching the old homestead(s) back in The Big Universe(s)?
>There's a strong appearance of the Trinity having pretty much given up
>on living or travelling Outside, and count on people coming to see
>them instead (hence all the techno-magic communication systems across
>the Void).
>

Keep in mind that they have a very tiny babby right now. :) They're building a home, but they've got more than a few places around town, as it were. Once Annabel's a little older, spending more time in Cephiro, Asgard, or New Avalon gets a lot easier. Even when you can move around magically, they still have a lot of stuff that has to come with them. :)

>Akio aside, does anything happen in the Diqiu universe when the Avatar
>goes off to a non-Diqiu-ish Spirit World, such as Valhalla?

That's one of the reasons why the White Lotus is so nervous about Korra going afield - nobody knows what would happen if something major went down while she was out of town. Or, for that matter, if anything happened to her.