The only one I can answer with confidence is that there aren't any earth embassies on Catia. So far it's just Kio's house that serves as the Catian Embassy to Japan. As of volume 14 of the novels, I don't think any of the other nations have actually gotten involved, except for the US, which occasionally gets mentioned as a sort of quasi-antagonist. They haven't been as hostile or active in the more recent volumes, though. I think the last big mention of them was volume 9 or 10.
A sequel would be nice, though I don't think this series was popular enough to get one. It's a lot of fun, and I enjoy it probably more than I should, but it is kind of "same-y" to a lot of other ecchi harem shows out there. I personally consider it a bit more refined, or at least not as trashy as, say, Ikki Tousen.