Welcome to the forums, Ancient_Lands.
AoM Gold Edition is simply the original Age of Mythology game bundled with the Age of Mythology:The Titans expansion. I'm assuming you just have the original AoM, so you can just buy the Titans expansion, you don't have to get the gold edition. The Titan's let's you play as the Atlanteans, has a new campaign, new myth units, god powers, etc.
There are plenty of fan created monsters, maps, etc in the downloads section
here
You can also download the official Ensemble Studios created mini-campaign The Golden Gift