If you want to go for the multiplayer route, I'd suggest going with another engine (Sorry, I don't know much about other engines, so I can't give a suggestion). I have not mucked around with multiplayer in C2 but I gather that non-realtime multiplayer might be possible, but realtime is out of the question. At least for the moment.
In regards to the second question, the best thing to do is start smaller. Follow the beginner's tutorials, read the manual, relevant tutorials, FAQ, and build up until you feel comfortable enough to build the game.