1. He has done so because of an upcoming quest to find and destroy Arawn's cauldron.
2. Awarn's Cauldron is a cauldron that can bring people back to life, but with consequences. Whoever comes back to life through this cauldron will become weapons of murder, pawns of Awarn. However, they won't have to experience death again.
3. Adaon is an insight and wise person, who can undertand people. He had a lot of experience from his past, like sailing beyond the Isle of Mona. This indicates that he is a valuable person to be travelling with, being quite wise and kind. He also has a brooch that can allow him to see the future.
4. Ellidyr might have been angry at Taran for not giving a proper greeting that he thought his rank should have. Technically, he was the one who started it. This arrogance may have started due to only have his name, sword, and horse. The little of Ellidyr's family fortune had been taken by his older brothers. Since he has nothing, he decided to become very arrogant as to cover up what little he has.
5. They are mortal servants that have chosento bound to Awarn through a blood oath. The Huntsmen are sworn to allegiance and are ruthless. They are swift and have a lot of endurance. Exhaustion, hunger and thirst do not matter.
6. The cauldron was given a new hiding place before the plan had been iniciated. Everything was fine, and the plan went exactly according to plan, but the cauldron wasn't even there, so all the hard work was for nothing.
7. Gwystyl is a thin man with a robe over his body. He has hair that looks like cobwebs, and his face has a nose that droops down over his upper lip which droops down towards his chin. He might be depressed because his job is boring and he's been on it for many years without a single speck of gratitude or payment for his hard work.
8. Ellidyr decided to find the cauldron, and that infuriated Taran, which led to them arguing. Eilonwy reminded that Adaon was in charge of both of the boys, yet the man decided that Taran should make the decison. He decided to go to the Marshes of Morva, and so that is why the company is going to that very place I just mentioned a few words ago.
9. There was a rock stuck in Islimach's left forehoof, and Taran took it out.
10. The brooch is a gift from Adaon's betrothed, who is unfortunately dead. It allows him to dream of the future, which is how he was able to foresee his death.