A list of all quests can be found at https://renryuu.miraheze.org/wiki/Quests
Keep in mind that some quests can be skipped. For example, Mira can give you a quest to go to the stone gate with angel wings in the north dungeon, but it's skipped if you went to the gate with Mira before talking to her to get the quest to do it.
No, there is no difference between the King or the Earl if you make Varea Queen in the end.
Thanks for the praise. I'm happy to hear that you like my game. :)