How to install a war...

[Arks]

Hello, I just want to get the ball rolling on this and keep it as short as possible... I'm looking for some advice on what the best way to go about setting up a series of NPC battles at random places on my server, since I rarely invite other players on it. Anyways, here's what I have in mind:
1. Create an neutral NPC that one talks to and clicks "Start Event".
2. Once started, the game spawns two armies of NPCs (roughly 75-175 units total?) on opposing sides of the area.
3. The armies wait a minute or so, such that you can choose a side.
4. The armies run towards eachother and battle until one side is annhilated.
5. Somehow end the event.

Can somebody outline the measures needed to make this happen? Please and thank you