Aaricia's title of Viking princess is based on Gandalf's title of king, but Gandalf became the ruler of the Vikings illegally, by usurping the throne after the death of the former ruler, Leif Haraldson. If everything was done in accordance with the law, Thorgal would be king instead of Aaricia's father, and Aaricia would not be a princess (although she would most probably wed Thorgal and become his queen). It seems that asserting that Aaricia is a princess implies opposing Thorgal's right to the throne. So, why does she so often say in his presence that she's a princess? (It doesn't seem to be very important to her, but she mentions it when asked or when it can be of help.) However, according to Jolan, Thorgal has never wanted to be a king of any realm - so, maybe this means that Thorgal acknowledged Gandalf's title from the beginning, treating his decision to leave the Vikings after Leif's death as the formal resignation of rulership?
In one of the stories in "Aaricia", it's shown that the high council actually acknowledges Gandalf's request for the throne, so his title IS legal. (although they do send one of their members there to keep an eye on him)
Thorgal's position was also always a little shaky because he was merely adopted by Leif and not originally part of the clan either, so the Vikings accepted him with reluctance, but didn't seem eager to take the passive Thorgal's side over Gandalf, who actually acted like they believed a Viking should act and who was more than willing to intimidate his opponents.
How exactly is it possible that the Thorgalverse is ruled by Fate and Norse gods, and at the same time has advanced technology and psychic powers as in SF? Does it mean that the gods controlled the development of the Star People, or rather that they only rule one planet - the one with the Vikings, their worshippers? The former option seems to be rather exotic in terms of worldbuilding.
At one time, Zarkaj said something about 'the gods of all galaxies'. If these are The Low Middle Ages, how comes that Zarkaj knows about the existence of galaxies if he is not a descendant of the Star People? Or, assuming for a while that he is one of them, does it mean that every galaxy in Thorgalverse has its own deities? That would explain much, but AFAIK is never told explicitly.
I always thought that he came from a Fantasy Counterpart Culture with an interest in astronomy, which would explain knowing about galaxies. As for the gods, well, presumably he extrapolated from all the pantheons on Earth alone.
The album "Kah-Aniel" throws a pretty big timeline screw-up into the mix. It mentions that Kahaniel of Valnor used to be the leader of the red mages less than a few decades ago, however "The Sacrifice" mentions that Manthor, Kahaniel's son, was born several centuries ago.