1. Can I duel and still participate in a quest at the same time?
Only if you received a judge and an opponent in the Challenge Section.

2. Can NPCs participate in duels?
That should be performed in an adventure. This place is meant for real players to battle against each other. You would not receive any rewards for winning in a battle like that.

3. Can there be two on two duels?
Yes, but anymore than that is not allowed.

4. Can we bring others along who aren't going to fight merely observe?
As long as both parties in the duel O.K. it then it's fine. They should not interrupt the battle in anyway. Like a baby grunty sitting on the sidelines. They can make posts if they’d like, but not large ones to loose focus on the battle at hand.

5. Can users bet on duels?
Yes they can in the Betting Thread: Here.

6. How do I calculate my character's SP and HP?
Character Stat Information: Here

7. How much SP do we regain each turn (Or post)?
Each of turn in the duel (including your opponents') you get back 2 SP.

What stats are important?
Your items have all kinds of state, but that's because the weapons are armor are from the original .hack Games. So what really matters your writing. More then anything!