All of this is (mostly) available on Area 51.
For example, one of the older 2.0 sites, Cooking (Seasoned Advice) still has their Area 51 project page:
All of the stats you're looking for, including their stats can be seen there.
While it generically says "public beta start - 7 years ago", you can hover over the date (as you can most dates) for the exact date information - in this case: 2010-07-16 19:00:00Z. Any site that has "graduated" will appear in the "Launched" section of Area 51. Unfortunately (as far as I can tell), the text that reads "This Stack Exchange site's beta was successful, so it launched N months/years ago." doesn't have any hover info with a specific date.
To find this information, you can search the Meta of the site to see the graduation announcement (Movies & TV). You can tell if it's graduated by whether it has a custom site design (for sites before design independent graduation or that have since gotten designs) or whether it lacks the "beta" wording in the site name (for those after). For really early sites, it may be easier to find the design launch announcement (Cooking) or look at the election history (Cooking), as an election is often the signal that a site has "graduated", with elections kicking off around the same time. The older the site, the less codified the process was.
As far as I'm aware, there's not any easy way to find these events without checking each site's meta. Such a page in the help center would be nice but, as noted, there's not always a hard date for these things, so it may be difficult to create such a page without having to create a table for them.
