the corn will have caves out, they just aren't all there yet, the lava is there to stop mobs spawning during the initial 60 seconds and killing players before the game starts, if you have another idea for how to do that i would be happy to consider it, perhaps using red stone lamps in the floor and turning them off at some point, I will look into it.
as for tripwires i have heard nothing about this, however the server plugin manages what is available in the chests so can't promise they will be in there.