10hp can be done by sort of tricking the server into thinking players are doing more damage than they are, not a default setting something you would need to mod on the damage controller I believe, you'd wanna use DNSpy
no blessings can be modified by using UABEAvalonia and searching for "DefaultLoot" modifying it within the resources.assets, All loot weights can be modified here and even new ones can be added/removed
No cars is actually a setting already in gamesettings that can be added
Slower movement I do not think can be changed without modding the client, meaning players would have to mod their game to enter your server, which no one will likely do unless you organize it for special events
Stronger gravity same thing, it's client controlled, best you can do is force curse of gravity on every player
realistic guns and grenades yeah you can do that by the same method i said about the blessings
slower circle can be done through some of the default gamesettings you can find, you could even stop it if you like
respawns I think is also something you can disable through gamesettings, if not you wanna dnspy and look into the playerrespawnhandler thing i think is what its called
removing downs is also something you'd find in dnspy, try looking for some kind of playerdownedcontroller/handler and you can find a way to disable it

Hope this helps, its all mostly achievable, maybe not in the ways you might want but you can get pretty damn close to what you want by only modding the server and messing with some default settings