I'm currently doing the same with Baldur's Gate engine. I am using Mootools, I want to study your code more to see if Dojo would be better (Mootools introduces overhead with constructors)
Basic demo here: http://lumakey.net/labs/battleground/demo1/
For multiplayer I'm making tests with Firebase...
Also I'm looking into WebGL for some animations (explosions etc) probably it could help performance in your case as well.