Here's how to get autofire, for all you lazy-fingered players:
Hold left mouse button, click right mouse button, press 's' to go to settings, click close, then you got your autofire.
Challenge 5: Yeah, natural gas is the way. Combine one or two of them with a few labs, then upgrade as soon as possible. Then sprinkle tesla coils liberally.
I suppose decades underground won't make you any whiter, eh? Also, they consume zombie offal? Foul. But its a great game nonetheless. Probably the most fun in a while on this site.