Getting Monsters to Spawn after another

I am trying to figure out how to get a group of monsters to spawn one right after the other after each set is dead, could someone give me a example ACS script that I could follow so that I can learn?. I have been looking all over the internet for the script lol.

You could give a TID to each monster group, and check if they're alive with ThingCount in a while loop (trigger the next teleport once ThingCount reaches 0).

Not sure what's the best way to spawn a bunch of monsters, especially if you want them to pop at specific locations and not in a tight formation. I'd just plop down each monster in the map editor at the positions I want them to appear, then select the whole group and move it into a dummy sector; and then use TeleportGroup.

I kinda wanna have it like doom 64 where you kill a set of monsters and new ones spawn IE watch your step and playground

Watch your step being at the end of the level in that big room you fight the monsters and then at the end you fight two cyberdemons

Playground has multiple spawns that happen though the map how would I do that.

I don't know Playground, but perhaps something like this:

http://www.mediafire.com/download/e1pn3io8u5scclb/zdoom_all_gone_02b.wad