I’m going out on a limb here and saying you’re using 3.0 from the way you’re describing the engine;
The thing you have to realize about the Event System is it’s a very helpful tool, however it’s no substitute for the quest system. In fact the Event System in 3.0 isn’t a complete one. You really need to use n version with a Quest System or add it yourself through source edits. Here’s how you would do it with the Event System (I don’t suggest it) and you can see why it’s not really wise to use it.
I. Collect X Items - You would use a Conditional Branch and Parallel Process to make a loop checking, if you had 1 item and take 1 item away. (Needs a source edit to check for more than 1 item).
II. Kill X Npc - This isn’t viable using the Event System. You would have to use Force Spawn Npc and use either a wait timer or activate an Event that needs clicked. Either way you can’t tell if you killed it or ran in circles till time was up. It would be best it dropped a quest item.
III. Follow/Protect Npc - Can’t really protect him, but through Switches, Wait Commands, and Switches/Variables you can create the illusion of a follow quest.
As you can see using the Event System as a quest System isn’t really viable.