Hya there!
We are set in Brittany, but since Damhan Allaidh features prominently in our saga, I and the beta SG have developed the whole tribunal of Loch Leglean. We also had an abortive saga in that tribunal, so I might help.
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LOTN
Amazing book, specially from a highlands point of view. however, the characteristics and abilities of the characters at the back of the book tend to be badly calculated. Some of the characters are even illegal (like the shapeshifter that cannot cast his spells because he has no Corpus score). use them for inspiration, but I would recommend not using them as they are, but only to inspire you at what kind of characters might be found there.
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CHARACTERS
Lord Goullis was never a character I liked, and I do not plan or planned to use it. A seneschal of the realm can be a pain in the ass without the need for him to be an infernal dude.
Gruagachan are cool, so yes, I planned to use them. If you are interested in more up to date approaches to them, you might be interested in the Land of Fire and Ice (the Iceland supplement) of ArM4. There you find information on trollsons, that are quite similar to the gruagachan in design. they are ArM4 characters, so their stats translate much better to ArM5.
Brude, yes, but not as a main character. He is the Big Bad grandpa of the gruagachan, so he should not be around most of the time. Idem with caitlin or other ultra-powerful characters.
- COVENANTS/HERMETIC POLITICS
We had 6 political divisions that split the covenants. We use the 3 featured covenants as the leaders of the parties:
A- Isolationist/interventionist.
The pact of cun clach is quite new (1189 IIRC) and not everybody is happy with it. Some magi want to be left alone and centre in their interests and stuff, while others enjoy the powerbreaking and making of kings. Some covenants and magi actively support the nobility in their struggles, while others frown on it. Remember that the pact only talks about kings, but says nothing about earl-helping. In general, the more continental covenants (vanilla covenants) prefer isolationist approaches, while highland or anti-Norman covenants tend to favour interventionism. This also creates a reaction in some pro-Norman covenants, that turns them interventionist, etc etc.
B- Scots/Normans/Saxons
This is the second big division. During the 11th and 12th centuries feudalism was introduced to Scotland. Coupled with the destruction of house Diedne at the start of the 11th century and the invasion of the Normans in 1066 have caused the tribunal to be a burning keg.
The Gaels that remain (non Diedne supporters of the Diednes) resent the helpers of the Tremere and Flambeaus; The native Scots (both gaelic and pictish in origin) resent the advent of the southerners (Scots and Normans) that did bring other social structures with them.
The Saxons hate the Normans, that came later and displaced them from the southern realms of Britain, and now menace them in their last refuge.
The Normans think all the above are a bunch of barbaric creatures worth only to clean their horse stalls… with their tongues.
No group is strong enough on its own, and alliances shift depending on the issue under discussion. The official covenants would be
- Horsingas: Saxon interventionist
- Cun Clach Norman isolationist
- Mac Gruagach: Scot interventionist
There are also the other options present (Norman interventionist, saxon isolationist, scot isolationist) for diverse covenants, with a total of around 12-17 covenants at any given moment in the tribunal. Makes for interesting hermetic politics. Going for a middle path is difficult, since you are likely to step on the toes of at least one major covenant if not 2 or more 
I will try to make a list of the covenants tomorrow. Disclaimer: most are blatantly stolen from sagas on the internet, since we have already enough stuff in our hands. Kudos to the real creators of the covenants.
- GIANTS
Giants should be a match for a powerful magus, specially if they are magical ones. I would use them as they are described there. Players tend top forget that you cannot always win by brute force. Giants are a good way to show them just that
Giants that are better suited for ArM5 coversion can be found in several ArM4 supplements, including the mentioned Land of Fire and Ice.
Hope that helps,
Xavi