As far as motors and servos I'd go for eight motors and at least a couple of servos. Most robots I've built so far don't have much call for servos, but almost all of the bots have used at least 6, 7, or 8 motors. 2 or 4 motors for drive train, 1 motor for each axis of movement on any arm built, 1 or 2 motors for elevator/lifting mechanisms. The servos that have been used were usually for pan and tilt mechanism for sensors like the ultrasonics.
As far as hardware... 1 or 2 gear kits 1 to 4 chain and sprocket kits (and more chain from vexlabs ala carte!) at least 2 extra hardware kits (or a lot of ala carte metal from vexlabs!) 2 omni wheel kits and 1 to 2 tank tread kits (they make awesome ball harvesting conveyors just check out any pictures of 2005/2006 Half Pipe Hustle bots!)
Just my two bytes worth.
