Hi had a quick test of the map, I think the cubemaps were not built into the map.
I think there are too many varied banners dotted about (or too many different styles).
The room with the circular columns is not a very good design, we try to avoid obstacles in the arena in which a player can hide behind or circle around. Would be better to fence between the columns and keep the players within the central area imo. Apart from that I like the style you've gone for.

https://dl.dropboxusercontent.com/u/38085756/ref/duel_box.vmf

Here's an example .vmf to help you figure out 2v2 spawns, note that smart edit is turned on for the 2v2 spawns. Duel maps also support custom intro scenes, you can look in berimbau\scripts\introscenes to see how they are scripted, but do not worry the default will be played in the absence of one.

I didn't know such entities existed. They'll go into b3 I suppose.

Looking good will add to my server when I get home tonight.
Did you manage to add teamspawns for 2v2 and 2v1?