To play online just get your GameSpyID and login in through the Multiplayer option in the main menu.

I tried to do it, but had trouble with the CD Key, as many people seem to do. I can link you to a thread if you have similar problems.

While I'm sure you are a talented enough player, you've probably got a while to go to beat some of the achievements other players here have made. In particular, Askthepizzaguy can capture a fully garrisoned Citadel with one unit of light cavalry, and can win Long Campaigns as the HRE in seven turns! The best I've managed using his tactics is winning as the Rebels after 12 turns (and there's a challenge for you, check the relevant thread here).

And while I've not played any M2TW mods bar the one mini-mod I made myself (in sig), SS and BC are extremely popular and I doubt they are rubbish. They look great from what I've seen in AAR's.

Anyway, welcome to the Guild!