Hello.

Little Issue: my opponent has 3 resource, wants to play for ex. grimgor's camp i throw hate. Do I have to play it before he decides to do so or can i do it in a response ?

You pay all costs for a card when you play it (i.e. put it on the 'stack'). You can play Hate in your opponent's Kingdom Phase, before your opponent has the opportunity to play supports/units, but if you pass this opportunity, you have to hope that your opponent can't spend all of their resources by playing one card.