Hi, good map. I think it could also work for 2v2. I have never made it Naxx in WoW so I cant compare it to WoW-Arachnid quarter, but to me it definitely looks like place that could appear in WoW.
Regarding gameplay, I believe you got almost everything right as far as I can tell. The only things I notice are:
-No buildable terrain near tavern, no trees for wisps near tavern and merc camps.
-There is enough buildable terrain near main bases and maybe also expansions. It is ok for 3v3, but in FFA, a common strategy is to bank a lot of gold and build much more producing buildings than in other gamemodes. You can see players having like 2+ producing buildings of each type, and several towers in their main and right now there isnt enough space for that, especially for nightelves who normally dont cut down trees.