Here's a few thoughts:
-Technical info like how many players for what bandwidth
-Max/optimum packet sizes based on bandwidth and players
-Potential lag based on where your players are, how to deal with it
-How to deal with dropped players, players disappearing etc.
-How to deal with drop in bandwidth due to network traffic
-Firewall/router considerations
-How to build/run your initial connection chatroom style thing
-How to handle open and closed games
-How to deal with different pings across your players and varying lag times
-Syncronisation
-How to deal with lost/dropped packets (programmer is expecting data that never arrives)
-Predictive motion (coding so objects/bullets etc. are predicting what may come in delayed packet data).
That's all I can think of for now. Hope that helps a little.