I run a game that regularly has 9-10 players at the table, each with a single character. The characters range from 6th to 11th level (worked up from 1st over the last two years). Some advice for running combat.
If you can, avoid it! D&D is a lot of fun as a combat-oriented game, but there's more to it than that. Work a little combat into every game for the fighter types and the tactical people, but focus on puzzle-solving, mystery, exploration, and role-playing.
Prepare for combats before the game starts. Not only work up the stats before the game, but also make notes about the tactics of individuals and parties. Work up attack bonuses by weapon and armor class. Don't just note the final numbers, but also the bonuses that went into it, in case you need to subtract a shield, or the fighter drops his prized +2 sword. You can recompute easily.
Appoint a player the Keeper of the Initiative. As you and players roll initiative, have the Keeper note them in descending order (with the rolled number). As DM, you just ask "who is next?" and the Keeper will tell you. He or she will also note what the character did each turn, to track when spell effects start and end and so on. This removes much burden from the DM.
Don't give players too long to figure out what they want to do. This is combat, not a chess game. If they don't know what they want to do within about 10 seconds, they're holding their action until after the next character; they can chime in when they're ready to act, or let their entire turn go by. Keep things fast and furious -- especially with spellcasters.
Don't get bogged down with special rules. Make a snap decision if you can't find the rule immediately and move on. If the player disagrees with you, he or she can look it up while you take care of the next person. You can always reverse your decision based on new information. (Sometimes, the ruling can impact several characters or the outcome of the battle, in which case a quick look-up is probably in order, even if it temporarily stops the game.)
Acquire a laptop PC and a copy of "DM's Familiar" or "Role Playing Master." Applications like these manage game information for you, and some have advanced abilities to be Keeper of Initiative and Combat. Check them out. Using these, large combats should be a breeze.
I hope this advice helps! Let us know if you learn anything that can help us!
Adam Dray /
adam@legendary.org