Greg's answer:
1. King Arthur Pendragon. Slept under a spell in the Hollow Hill.
2. Merlin. Son of Oberon by a mortal woman. Imprisoned in the Crystal Cave.
3. The Lady of the Lake. One of the Oberati.
4. Sir Percival. The Fisher King. Mr. Duval. Founder of the Illuminati. Spends a lot of time in Castle Carbonek, a sort of mini-traveling-Avalon, where time passes differently. Also uses the Holy Grail to maintain his youth, though at a very real physical cost, due to his, shall we say, sins.
5. Lady Blanchefleur. Percival's wife. Queen of Castle Carbonek. She lives there and uses the Grail. The only cost being her estrangement from Percival.
6. Morgana le Fay. A changling in the old-fashioned sense.
7. Nimue. A sorceress with connections to Merlin, the Oberati and Morgana. (Think about it.)
8. The Green Knight. An Oberati.
2. Which female Arthurian survivor would accompany Arthur on his quest to find Merlin?
Blanchefleur.
3. Does Arthur eventually seek out the Holy Grail?
After he finds Merlin, yes.
4. Did King Arthur have any adventures between "Avalon" Part III and "Pendragon?"
Yes, he had one unseen adventure. Then he returned to Avalon and considered staying there. He decided against it and went into the mists again, which led into "Pendragon."