Here is the necessary information you need in order to set up a basic server for Screaming Steel 1914-1918.
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Playlist paths:

ww1/mp_battles (Pure PvP)
ww1/mp_battles_bots (PvP with bots filling empty slots)
ww1/coop (Regular Co-op)
ww1/coop_commando (Commando Co-op)

Starting map + gamemode for PvP: somme liberation
Starting map + gamemode for Co-op: nimy stronghold

Workshop ID's:

1454108722 (Main Screaming Steel files)
1095516761 (Somme)
1170130416 (Passchendaele)
1170132122 (Nimy Bridge)
1170133655 (Valenciennes)
1390091959 (Givenchy)
1794424985 (Bailleul)

Alternatively the official Workshop Collection ID can be used: 1455070029

In addition to this, it's recommended to add these commands to your server startup command line and your server.cfg to prevent issues.

sv_pure -1

mp_theater_override ScreamingSteel

(And one of the below, depending on the type of server you want to run)

sv_playlist ww1/mp_battles
sv_playlist ww1/mp_battles_bots
sv_playlist ww1/coop
sv_playlist ww1/coop_commando