Welcome to the community. I don't play MP but I'm sure you will have a lot of fun destroying other community members.
I really like Glory of the Gods (multiplayer, 224-province version) but lately I've become a fan of the wraparound maps. I also like the United States map
here (at the bottom of the page).
No real opinion on the mods, although I had fun with Mythology (more pretenders) and have heard good things about Worthy Heroes (more nations get worthwhile heroes). Conceptual Balance Mod has a good rep among MPers. Mostly I mod my own stuff as I feel like it (I think the Wyrm should have recuperation/healing as well as regen, for instance, and my Vampire Queen is ethereal). I keep a "houseRules.dm" that is always included, so that if I need to make a fix to a game in play (e.g. turning off independents) I can do so without restarting the game.
I do recommend Edi's "Better Independents" mod, since armies of national troops are more thematic in my mind than hordes of generic independents that you sometimes see otherwise. (I hate it when Yomi or Niefelheim invades me with... 300 Light Cavalry. Where are the demons and giants?)
Mostly, though, I would recommend playing vanilla until you feel like you need mods.
-Max