You can find this information on https://state.disroot.org which is also a page where we inform on issues, scheduled maintenance and downtimes.
The version information is at this moment fill-in manually so sometimes (just updated it now) things might be slightly out of date (minor nextcloud version for example). We do not put versions of each nextcloud app but as soon as we automate the process of adding versions we will.
As for frequency of updates on nextcloud. As far as Nextcloud major releases go (for example nextcloud 16) we do wait a bit (sometimes until .1 release) before we update, unless everything on our test instance runs without problems right off the bat. With minor versions and apps we tend to upgrade within few days (usually do it over the weekend at night to cause as little noticeable downtime as possible).