It occurs to me, how do we want to adjudicate duels? I don't see anything in the OP yet.
1. Play through the duels on the forums.
>Pro: No extra software needed (except a die roller). Flexible.
>Con: Slow, cumbersome. Prone to breaking down if/when players drop the game without notice.
2. Play through Duel Network or DevPro (or other YGO Pro clients).
>Pro: Quick, efficient.
>Con: Have to get some other program working for YGO Pro-derived clients, or register on another site for DN. May not work for all players. Players must be online concurrently. May not be able to conduct a tag duel or battle royale.
3. Abstraction. Give players basic stats (like Power, Technique, Money, Heart/Topdecking, Cheating, etc.), roll against these to see how each turn (for major duels) or the duel (for mook-beating) goes. How the turn works out goes into fluff.
>Pro: Don't have to worry about the card game itself - can focus on RP. Random chance still plays a role.
>Con: Have to build a stat system from scratch. Random chance still plays a role. We may actually want to play the card game, being that this is, you know, an RP about children's card games.
4. Pure free-form.
>Pro: We have a mature player base that won't likely descend into bickering. Story-driven - duels can go in a manner that makes the story interesting, instead of going off the rails because the big bad couldn't draw a monster for ten turns.
>Con: Potential for accusations of god-modding, arguments still exists.