So, the core rulebook lists the AT-EST, but I have been unable to find any info or pictures of it anywhere else...
If nothing else, I'd just like to know what the thing looks like...

Six legged and low slung sounds that it would look like this.

http://starwars.wikia.com/wiki/All_Terrain_Tactical_Enforcer?file=AT-TE_TCW.jpg

I would guess that a smaller and lighter AT-TE would fit the bill nicely. Well spotted Jetpack.

Excellent.

I don't have my book with me but I think it says that its basically a smaller, less heavily armed version of the AT-TE. Or something along those lines.