ATTENTION: HEY PEOPLE !!
Generally:
IF you want to have your server full of happy gaming people just install (english version ofthe game and update to postal2 1409)
and that's all don't install anything else or it will change packages and people wont connect to your server.
for those a bit adnaced of you:
Of course there are some stuff you can install and use download option in your settings for people who dont have it in their games but you must be careful whith those like i said
One of best ideas is just to go to any of those webs about postal2 and donwload some maps or any addons whith this case in mind.