I was trying to host server with SDK on my pc and here is everything I found:
- SDK is downloadable tool from Steam, can’t be downloaded from other sources due to SteamAPI dependencies
- It’s running on DX9 like usual game, just limited to multiplayer hosting pitboss (client looks like game observer, might even see whole map and all stats)
- Minimal requirements are about equal to usual civ5, so running it on cheapest, non-gui server won’t work (2GB Ram, 8GB storage shouldn’t be a problem, 256MB Vram, 1.8GHz CPU)
- To make SDK even work, it must be moved to game location / must have game files in the same folder (need more research about dependencies)
- SDK uses the same config file from MyDocuments (DX9 version), so you can lower to maximum settings in game (obviously DX9 version) or just dig in config (yes, there is window mode and resolution options, but you should be careful with those, due to UI problems like buttons are not in window etc.)
- Only way i found for lowering requirements of server (not tested on real game!) is just ape-like not allowing app to use every possible core (that’s in Task Manager), but it still sucks about 15% power of my i7-6400, so i guess that’s pretty much for lowest settings
- To set up server you have to open few ports on your router, depending on it’s manufacturer it might be easier or harder
-
YOU CAN’T OPEN CIV5 WHILE SERVER IS RUNNING, EVEN IF THEY ARE IN DIFFERENT LOCATION 
(some VM might be helpful, didn’t test it)
After all, I didn’t decide to host server due to restarting Civ5 all the time (as I said, VM doesen’t suit me).
Sources:
https://forums.2k.com/showthread.php?272271-Pitboss-Instructions - Official discussion
steam civilization 5 - How to make a dedicated server work on a remote server without a GPU? - Arqade - Haven’t tried it, didn’t have spare server to do so
also some reddit links, but basicly everything needed is in those links