RE: Gardevoir=Gardevoir ex??
Pokemon-Ex are considered completely different from normal Pokemon. As such, you can run up to 4 Gardevoir and 4 Gardevoir Ex.
Light, Dark, Rockets and all that stuff is also counted as a different name. For example, you could have:
1 Charizard*
4 Charizard
4 Charizard Ex
4 Dark Charizard
in one deck. The only exception to this is LVX, but you should see it like the regular LV so many, which you find on the cards (ergo, Gardevoir LV55), just replace the 55 with X.