1. What will I need networking wise?
Switches that can handle the load....I don't know the specifics of this but we generally did up to 15ish people with just our household routers running as switches.
2. What snacks do you recommend?
surprisingly healthy things help people go longer duration, however they are not very desirable. If you are all of the age, good beer is always in want.
3. Best LAN games?
My new favorite lan game of awesome: http://cutstuff.net/mm8bdm/
We also like any other DM game, specifically Goldeneye Source, Primal Carnage, TF2 and so on. For a lite game, http://armagetronad.org is always a fun one as well. Try to be creative as well, and if things get a little tired, get everyone up for some game to move and such...Have options, but be prepared to play TF2 all night long.
4. Any other tips for an enjoyable experience
Clean...Clean before, clean yourself(Read As: Shower) clean halfway through, clean after, your day will be much easier. Don't let trash pile up.
Prepare, make sure servers are running and stable(even if just you is running) all games are up to date, you have the installers for things like armagetron, mm8dm, and Goldeneye Src.
Ambiance, a bit of light trance or something in the background, rather quiet, so that people with crappy headphones can't hear it when they're on, gets things going. A light level appropriate to your group. Some are near pitch black, some are low light. some are high light. Plan accordingly, if you're going to have power cables and stuff running all around, be sure to have some lighting.
Generally Googling "LAN party tips" or something of the sort gives 500 million billion queries and the first few are on LAN party websites that have information. I think lanpartguide.com was mentioned above... its a good one
One last note, If you can, attend a large LAN party before, or before your next party. See what they do right, do that. See what they do wrong, don't do that.
Edit to fix obnoxious spacing.