I wanna ask you few question

1. Can you tell me the different between the cvar abm_respawndelay and abm_spawninterval
2. I want my server like this. Always have >= 4 survivors bot for 4 players to playing on it. When the 5th player join the server, it automatic create the 5th survivor bot for 5th player. Do the same with 6th, 7th, 8th,... player. When a player leave the server, it automactic remove the bot which that player have played. So what should i do with those cvars?
3. The different between abm_autohard "1" and abm_autohard "2" ?
Thx you very much
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I am a noob so... hope you guys will help me up

P/s .-. : My English is bad, i am good at Vietnamese