3 multiplayer questions
 

what does the M/C under teams a and b stand for? Why do you get directed to a game and it will list up to 16 players, only one player on list, and you leave session? Is there some issue between xbox consoles that is causing this or what?

M/C/Bx stands for the loadout you're taking. M is for machine guns, C for cannons and B (sometimes with a number) for bombs, where the number indicates the variant. The La for example shows only C, because it only has cannons (and B as well, if you select bombs).
I'm still not sure. My guess was that it's because the countdown started already, but if there's only 1 person in the lobby.. It could be a ghost server, where the host lost connection accidentally and the game didn't close the lobby properly, showing a lobby where there actually isn't any.

^ There's also R for rockets :)

I think when you can't connect to a host it's because either he or you (or both) have ports blocked by a firewall and/or the ping between you is too high for the game to allow. Although I doubt the latter because you get some pretty laggy games...