Put the wiki wherever your community is right now.
If your community is here, then How to create a Wiki Post in Discourse
Build the wiki you need to collaborate for 18.04. That’s the immediate project goal.
You can always migrate content later as your tools and workflow change.
The community hub has plenty of Admins and Moderators willing to help you migrate, and to close out old stubs and erase mistakes.
The project leader has already said what he wants volunteers to start working upon:
Time to hit those aim points. Then discuss more.