Hi Bearklaw
Thanks for the questions.
- It is ultimately up to you whether reactions should be rolled each time or not. If an encounter's reaction is obvious to me (like if someone is already an enemy), then I go with I think is best. If it isn't obvious to me, I let the dice decide. Most of the time it isn't so obvious and I think that makes things more interesting.
- Ultar isn't really a person anymore. He is a force of will kept alive through supernatural means. In his description it says, "He cannot remove his armour, for there is nothing inside except a raging will for vengeance." All he wants is to destroy Fyr's heart, and he will do anything to achieve that. If the PCs can convince him that he needs their help, then he would ally with them. If he sees them as threatening his chances at destroying the heart, then he might mark them as an enemy. For a more behind the screen view on things, he is the unstoppable force and Fyr is the immovable object. They are opposites and in stalemate.
- Yes, I think I do need to define her forces a little better, but they are all the "dark forces of the forest". This equates to all the creatures and things that have been trying the kill the PCs. I had in mind that the barkfolk can be radicalised to fully side and fight for Fyr, unless convinced otherwise.