Just some notes on hosting a server.
This is a list of links and steps to customize the server. Based on a VM/server, docker could also be an alternative...

Start with your basic OS of choice.

Then continue by installing "Linux Game Server Managers" for Insurgency Sandstorm Server, to keep things clean:
https://linuxgsm.com/lgsm/inssserver/

XP

To be able to support XP play you need to register server here and copy the token to the config.

changes to inssserver.cfg:
add variable for token "gslt", and add: -GSLTToken=${gslt} -GameStats to the startup command.

Cronjob

This one monitors if server is running every 15 minutes and reboots if needed, checks for update every 30 minutes, validate at 9AM, Backup server 10AM and restarts the Game server every 6 hours. Starts the server at boot. (ref)

*/15 * * * * su - inssserver -c '/home/inssserver/inssserver monitor' > /dev/null 2>&1
*/30 * * * * su - inssserver -c '/home/inssserver/inssserver update' > /dev/null 2>&1
0 9 * * * su - inssserver -c '/home/inssserver/inssserver validate' > /dev/null 2>&1
0 10 * * * su - inssserver -c '/home/inssserver/inssserver backup' > /dev/null 2>&1
* 6 * * * su - inssserver -c '/home/inssserver/inssserver restart' > /dev/null 2>&1
@reboot su - inssserver -c '/home/inssserver/inssserver start' > /dev/null 2>&1

Game.ini settings

;Respawn player when it counter attack
bCounterAttackReinforce=False
;DPR is counter as amount of bot died before it trigger the spawning
;Example 0.2 = 20% of bots dead before it respawn the bot
;Set DPR to 1.0 = 100% of the bot died before it respawn the bot (However, that seem to bug out so setting 1.0 is to stop bot from respawning)

Resources

Details on setting and source for a starter Game.ini:
https://github.com/zWolfi/INS_Sandstorm

Some details on co-op:
https://steamcommunity.com/sharedfiles/filedetails/?id=1583049807
https://steamcommunity.com/app/581320/discussions/1/1743353798893925122/

Settings explained:
https://drive.google.com/file/d/126TRVf2Hy8v1pFhIj4tLoYP9pyhYge3y/view

Docker alternatives:
https://github.com/bugparty/insurgency_sandstorm_docker
https://github.com/hyperbolic2346/sandstorm