1) Is this going to be 1 big room or a complete castle with starting points for everyone?
1a) If it's a big room, what will the dimensions be? If you could even throw a pre-description out here that would be great.
2) Preparation stuff...
2a) Will everyone start off with protective spells cast and/or armor on or will eveyone have to start naked? I can see how a spell caster will have a problem with me (or anyone else) that has armor on before showing up to this battle. They may want to cast some spells (Mage armor, shield, etc.) to help them out before us fighters start hacking at them.
3) Detect magic spell? I'm guessing that the spellcaster will cast detect magic to figure out what's magical and what's not. I can see this as being a problem with describing what they see of if they don't want everyone else to know what they see.
4) You had mentioned that there is no teleporting, but what about teleporting, dimension door, etc within the castle?