Probably be forced to update while I'm sure you could get away with running it on a slightly older version our official recommendation is to run a style version equal to your XF. If XF adds or changes things in templates that we edit you'll be running those new edits which may not be in your version of XF
Fixed I'll be pushing the new update to the demo board this weekend then shooting for a release shortly after that.
When I started these child styles I realized customizing the sidebar was... difficult. So the main Archon style will ship out with a different sidebar, then one of the child styles I'm shipping out with it will have the original Archon sidebar.
Yes it's finally ready , I'm wrapping up a nice XenBase update which improves on quite a bit of things as well as adds a few nice functionalities to it which Archon is ran on. Once I get this finalized I'll push Archon to the store.
The sticky sidebar is fixed in the final release so you'll be able to use it on any page. The sticky JS wasn't activating on pages that normally didn't have a sidebar in XenForo. Ideally though you'll want to use the widget framework along with this style to populate the sidebar. This is finally shipping out with our next XenBase update which is almost there.