There are plenty of people online.  Get online and hang out for 15 minutes or so.  Even at hours in which few people are on, that should be enough to find a game.  Worst case scenario, you go to the multiplayer organizer section of the forums and schedule one with people.

Yeah... might want to play a bit of single player first though. If you play the large team games someone is bound to get mad at a new player for "costing them the game". And be prepared to lose a lot of course.

I don't know if coordinate is the best word, but you definitely have to work with your teammates. The main thing that determines your starting tactics is your position, since on the random maps that usually get played all players get randomly positioned in a ring. If you have two allied players on your flanks, you're expected to expand towards the center ASAP, expand your economy and eventually start giving resources to players doing the heavy fighting on the flanks. Also, if you notice an enemy player is wedged between yourself and another ally, the two of you should probably rush him ASAP and take him out quick.

If you mean before the game even starts, not really, as the mentioned random positions makes making a plan pretty much pointless until you see where you spawn.