A question regarding the terrain tool.

A few actually. Firstly is it possibly to create large caverns and tunnel systems. Im talking really big. Basic gist for this is that what I am wanting to do is to build a large underground city with large caverns and tunnels that connect to other caverns. Question two is sort of a branch off of this one. One of the components of a the rock in the cavern itself is that there is a type of crystal that forms on the rock that gives off a bright glow. So I was wondering if there was a way to create a paintable texture that has veins in it that give off emissions from just the veins/specified area. Any help would be very much appreciated!