I have seen some of the maps, and noticed they're symmetrical. Is there some sort of program that does that (Like SCMDraft for Sc1), or do you do it on your own?

You can copy, rotate, and paste doodads and terrain. So you make half the map an then copy it, rotate, and paste it. Bam symmetry.

Yup. While on the Terrain layer, hit 'Spacebar' (I think, to remove current selection/tool), this gives you the 'Selection' tool. You can 'Box' a part of the terrain and then go to Edit>Copy and use Edit>Rotate or Edit>Paste to whack it back down into the map. It haz hotkeys also but I can't remember them.

Also, you have to do Units, Pathing, Doodads, Points and Regions separately since they exist on different layers, but essentially the same process works.