FGD file for missing weapons
An FGD file that contains entities which are missing in the original Alien Swarm swarm.fgd but are present in source code and can be used in Hammer.
https://sites.google.com/site/swarmaddons/utilities/swarm_fixed_ents.7z
Put the file into ...Steam\SteamApps\common\alien swarm\bin\. Run Hammer and add this FGD file into Hammer settings dialog. You will be able to add weapons like minigun into your map.
Respawnable weapons and ammo
An example VMF file that shows how to make respawnable weapons and ammo in your Alien Swarm map:
https://sites.google.com/site/swarmaddons/utilities/respawnable_weapons_and_ammo.7z
Navigation mesh test files
These test files show that NAV files are not used for AI in Alien Swarm. See this thread for details
test_nav.7z
test_nodes.7z