It would be good to clarify whether this group aims to work on anything related to mediawiki.org. You talk about "Foster the ecosystem around MediaWiki" and "Improve documentation of extensions and MediaWiki visibility". These are noble goals that will need the help of mediawiki.org as a promotion tool. Editing pages is fine, but what about more complex developments needing community consensus, such as changes in the homepage or the skin, or a catalog of extensions? I don't have a specific answer, but overall I think it would be good to agree that this group should have a say about the evolution of mediawiki.org as well.
Topic on Talk:Groups/Proposals/MediaWiki Cooperation
In our September meeting, we agreed on the formula: "Sometimes mw.o isn't up to the task of achieving goals of MediaWiki Cooperation, so we need to have a say". Essentially, that means we need to work together with the mw.o community to achieve our goals. IMHO, ideally, we are part of the mw.o community :)