How do I stop Spawn another object from spawning numerous copies of the chosen sprite?

I think what is happening is that you are calling the Spawn action on a Sprite instance, expecting for a single Sprite to take the action.

What is likely happening though, is that all the sprites picked in the corresponding condition are doing the Spawn action.

You need to make sure you only pick the instances you need. That depends on what you are doing.

I took a quick look. You were just misusing the Wait action.

Here is something more like what I think you want.

dropbox.com/s/3i129jqgxbnbeia/Zeltronics%20VOZ%20%281%29.c3p

Check out the part using the Every X seconds action. I also added a little change to the main layout so the game could start without going through the intro, so be careful if you just copy and paste stuff.

Here is a short tutorial explaining the Wait action better.

construct.net/en/tutorials/system-wait-action-63