SC2Mapster

You can select the Barracks in the condition when the left value is a "Unit Type" function (or value) then you can put any values on the right (including every units in the game)

Oh yea I forgot that part, you can use the "Remove Unit" function or "Kill Unit" function to remove/kill units. The main difference is that removing will just make the unit disappear like it never existed, and the "Kill Unit" function will kill the unit just as if it was killed by another unit.

You can use variables dimensions for multiple switches for multiple player. Dimension is an array type variable. So for example, without dimensions the variable would be:

Switch = True

With dimensions you can do something like:

Switch[3] = True

Then instead of :

If Player = Player 1
    Switch1 = True
If Player = Player 2
    Switch2 = True
If Player = Player 3
    Switch3 = True

You can write:

Switch[Player] = True

Because "Player" values in the Galaxy Editors are Integers

You can use the "Unit Training Progress" event.

As for your toggle/switch, yes I believe what you want is Variables. You can use "Boolean" variables which can have only two values: True or False. So you can just set your variable to True when the special unit has been created, and then check if your other conditions are fulfilled, in order to activate a Trigger that would spawn your unit at a constant interval.

Here's an example of what I understood about what you want to do: http://i.imgur.com/kHmhB9W.png

Hope it helps