[Nicol Bolas]

+ttt_happyhome (a good size for 32 players, good variety as far as verticality and size goes)
Map description in the workshop itself only recommends a maximum of 10 players for this map. There are only 16 player spawns as well, but this is an easy fix regardless.
+ttt_poolparty (a smaller reimagined version of popular map ttt_communitypool, would work well with 32 players)
Poorly optimized and exploitable.
+ttt_mw2_terminal (great size for 32 players or just 16, fun times with explosive barrels and has something for everyone)
Too easy to map exploit without serious map editing.
+ttt_islandstreets (no joke when I say this map's not only one of the most visually stunning maps for ttt, and gmod in general, but is excellently balanced and I have no doubt it would perform well with 32 players)
Poorly optimized for multiplayer and causes extremely bad performance issues even on my computer.
+ttt_port (similar to islandstreets, a solid map for balanced gameplay of all sorts, with something for everyone.)
Also suffers from poor optimization.

I'll respond to some of the maps I've already tested on the test server.

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Also I find it funny you say bikini bottom is too small then proceed to suggest 4 maps that are the same size or smaller.