Well, my suggestion would be to start here
http://www.crymod.com/board.php?boardid=195here
http://www.crymod.com/board.php?boardid=88Good things there. Now, as for height maps goes, we DO have a height map program avalible to team members called Geocontrol2 (fantastic little program, sometimes has a bit of downtime between builds as it's in beta still, but it's really helpful). I'd suggest doing what you can, and perhaps learning some basics of making height maps. If/once your on the team, you can get setup with geocontrol and make a much better version, but if you can just get in a very basic height map for now, and create a fully functional multiplayer map (with ability to spawn players from each team, 2 headquarters and 2 outposts, and preferably buy zones). Get as much artistic work into it that you can, since we really just don't have enough level designers to spare for working on other peoples maps.
Now, as far as laying out the maps, or what we are looking for, we really have no real bounds on what mappers can do, as long as they stick to the idea of 2 bases, 2 outposts, and battle line combat (each capturable site will require that previous sites are already captured). Now, this is kind of a double edge sword, in that this gives mappers a lot of freedom, but at the same time gives them little guidelines to work with.
Now, this also means no limit on theme of the combat, so if I was you I'd try and make the objective points make real world sense. For instance, in Extremity, which Wormslayer is working on, is based on being a mineral mining operation under invasion. The Clan base is a small vehicle bay which has been overtaken by the clan via dropship (thus, creating the Clan base) and the IS base is a pre-estabilished base built into the opposite side of the mining valley (a giant crater, about 7-8 km wide). Each outpost is an actual stratigic goal, one being the mining center, the other being a solar collector(Though I think this changed to another site of equal importance, as we already had a good asset that fit the senario). You could take an idea like this, but perhaps get inspiration from historical battletech fights or skirmishes, perhaps re-telling the story via your map. I'd say, make the map like you'd make a mission for CBT, since thats basically what it is from the level designers point of view. You want each side to be evenly balanced (perhaps not mirrored, but balanced) and likewise with the terrain layout and possible tactics. As far as THIS topic goes, I'd also suggest reading the article that I'm ATTEMPTING to attach

. Excellent read to say the least.