[Otaku]

Make sure the network is set up properly, and there's enough plugs. You can pull up to 1800w from each outlet on a plug (120v / 60a), so you can get 2-4 computers on a single plug (but keep it down to a minimum if at all possible).

To give you an idea:

Tech High has 80-120+ person LAN parties every few months and there hasn't been a power issue in three years (and even then it wasn't that bad, one circuit broke and shut off my computer and three others, but that was it).

Speakers are fine, but if you DO allow people to bring them (which you shouldn't in this case), make sure that the attendees collaborate and share speaker time OR play music everybody likes.

Hope this helps.

-Otaku