Hello all, I just found Ars Magica (4th Edition) and the Loch Leglean & Stonehenge Tribunal books at a Convention so I bought it to see what kind of game it was. This far I really like it.
I am about to launch a small campaign in this game and I wonder if there are maps somewhere of all official covenants in Loch Leglean, Stonehenge and Hibernian Tribunals, because that would be a great help for a new GM?
There are no "offical" covenants in any of the tribunals you mention, in the sense that canon was reset at the start of 5th edition and none of these tribunals have been republished in that edition (although Hibernia is next up, in The Contested Isle.) Well, Cad Gadu exists, there's a Criamon sept that can make regiones on the Isle of Arran, and there's a large Tremere covenant that might or might not be Blackthorn. That's about it that I can recall.
A lot of people use the covenants in Heirs to Merlin (4th edition), Lion of the North (3rd edition) and a two page spread in Order of Hermes (2nd edition) as a starting point. How useful to you they are depends on how you want to use various ideas which have changed since. So, for example, the most powerful maga in LL in LotN is technically not a magus at all in the new editions, the Tremere work differently than in HtM, and so on.
What I'd suggest is that you work out what story you want to tell and build up from there. If your players want politics, build politics. If your players want a war, then have a Scandinavian invasion aided by the Scots/English/whoever. Get your characters and covenants together and then build up.
Heirs to Merlin is the last tribunal book for 4th edition, and was written by David Chart, the current line editor, so can be considered almost-official for 5th edition. Most of us consider it as such when we talk about England and Wales. Having no stats simplifies that usage even more.
Lion of the North is a superb supplement, but old. In older editions the tribunals were way less detailed from the point of view of Hermetic landscape, so you will only find 3 covenants there, the leaders of the 3 main factions at tribunal. I would suggest checking the links in redcap.org, the Ars Magica wiki. There are quite a few linked sagas there set in Loch Leglean that have lots of ideas for covenants. I would suggest quite a few covenants (12 or so), but most of them being small and weak (spring and winter) and most magi being exmiscellaneas and/or living on their own. Lion of the North contains the story of the war against Davnalleus, what makes me believe that JK Rowling plays Ars Magica since he obviously inspired Voldemort from the Harry Potter series He is the favorite arch-villain of my gaming troupe and the war against him is one of the coolest story arcs ever. Davnalleus can be created very easily using the Damnhaid Druidsan from realms of power: infernal for 5th edition or using the gruagachan rules from hedge magic revised edition.
In any case go for names and small descriptions. You do not need a lot of material early in the campaign since the player magi are likely to have few info on them if their tribunal lore is low. Get a general playing grid in your mind and that is enough. Most adventures will not bring other magi to the forefront anyway.