Campaign Creations

I've started making a Diplo-clone for a space setting rather than the usual world or Europe map. My problem is two-fold. First, I can't figure out how to get the money giving triggers to work properly. Second, I'm trying to allow players to buy a special unit, but they may only have one at a time. When I try to do this I can't get the triggers to make the chooser (Terran Civ.) to disappear when the unit's alive and then come back only after the unit is dead.

And as an aside to all that, how do you use switches?

For the 2nd trigger you could do a switch like Player X commands exactly 2 of the unit you only want 1 of them to have. Then have that move the civilian to wherever or make a new one, and have the trigger remove the 2nd unit, and give the resources back. Then have a message that says you can only have 1 unit at a time.