Are there any quests that I can miss?
For most quests you can simply go back if you've missed it. The only exception to this is a questline belonging to a faction that can either be friendly or hostile.
This applies for the following factions:
Vanilla
- Kymon's Chosen
- Orther of Death's Vigil
- The Outcast
Ashes of Malmouth
- Barrowholm
If you chose to become enemies with one of the factions mentioned above you will not be able to play their questline in the current playthrough.
This means you can still become allied with them in a later playthrough though.