Also, reading some actual plays or session logs might be helpful for you as well. You can find individual covenant write ups on Project Redcap, though which ones actually have session logs or actual plays you would have to find searching them one by one. I did post a related thread to find some of these for the actual play forum on this site. Note, I do have an actual play, however, I don't know that it is the most useful thing because the style of game I'm running is rather atypical for Ars Magica Campaigns. (And I voraciously read every single covenant on project redcap back in the 90s. Though not in some time have I looked at what is new there.)
Even without a Tribunal Book, you can find loads of other groups' covenant write ups on England. It is one of the easier areas to find resources for. @KevinH recently posted an entire custom StoneHenge tribunal.
When it comes to what books to use, I agree with the large sentiment of what others have said here, for the most part you can use these as you need them much later. Starting with core and maybe Covenants (as I quite enjoy the book!) is about all you need. The House of Hermes books do flesh out the background of each house quite nicely. I also agree that Mystery Houses and Mystery Cults add a whole new layer of complexity that a new group should probably avoid. Many of the other books are situational.
For my current 1st Crusade campaign, I make regular use of:
(1) reputation/prudhomme & agency rules from Lords of Men
(2) Example Jinn from the Tales of Power
(3) Sahir rules from The Cradle and the Crescent (as well as using the charts for Persian and Arabic names)
(4) Summoning/Binding/Commanding Rules from Realms of Power Infernal
(5) Invisible Fighting rules for HoH: Societates
So, I don't even technically need the entirety of each book, just some key pages from each one.