Welcome Morindin,

For MP purpose, most players are on VI 2.01.

With RTW coming, it's likely that in 2 or 3 months there will be few VI players online, and most players will have moved to RTW. Up to you to see if it's worth it.

I play mostly MP, 4v4 battles are more fun

I'd say the AI is somehow better than what most people say. In SP campaign, the strategic part is too weak, so AI armies are overpowered and gives the AI a bad name.

In custom game, AI is a bit better, provided you pick the right troops for it. I found the AI weak for handling missile units, more specifically x bow, arbalest, and hybrid warrior archers. But for everything else, it's quite good, better than its reputation.
To see the AI at its best, go for custom games, gives the AI archers and longbows for missile. You can play custom 4v4 games with the AI; very funny, as the AI got a very specific sense of teamplay

Good luck and have fun,

Louis,