Factory build - a source mod idea

Imagine a mod where you and a few other friends fight off waves and waves of NPCs. NPCs being combines. You can loot their corpses for money, medicine, heath kits or ammo. It can be played alone but it's most fun in co-op where 4 players work together.
Each one of them have a deadly sickness though. They are fending off the enemies in a bioweapon factory and have all been infected.
Every 5-10 minutes they need medicine to stay alive.
Medicine, ammo, weapons, healthkits and building materials can be purchased off vending machines in each corner of the factory. To afford medicine and the other stuff the player must kill and loot enemies.

Why I think it’s best that way is because then the players won’t just camp in one place. You are able to barricade the enemies out for a limited time. They will eventually break through your blockades. You can use your gravity gun to build just like in sourceforts, but can’t just camp in one place.

Either you win or you loose.

Now here’s where a 5th player comes in. One player will be controlling all the NPCs from an over-the view view the map. Just like in an RTS. The factory will be 5 stories tall and feature various obstacles and blown-up walls.

The person in the RTS view only has a limited number of NPCs at his disposal. Ca. 500.
Once they run out the 4-player team has won, and opposite.

The RTS view character can only have a limited amount of NPCs sent out, but that number will increase once the wave number increases.
This makes it more balanced.

If the RTS player is AFK for 40 seconds or more he will be kicked and a bot will take over. If another person joins the server he will take the RTS player's place.