While most of the advice in this thread is good, I would suggest reading Velusion's Ermor Stregy guide before playing them it in MP. While the guide might be a little out of date the concepts are completely valid and nessesary for Ermorian victory. I have used those guidelines to acheive status as a major world power as Ermor, and you can too. This is the link:
http://forum.shrapnelgames.com/showthread.php?t=35061