one simple question
 

Can i use older mods on newer versions of vb. Like 3.0.4 mods for 3.6.4, lets say.

You can use them but depending on what's changed in their code they may not work. The newer the mod, the more likely it is to work.

I would suggest against it; especially, if you don't know anything about scripting or vbulletin's functions, etc.

The oldest mods that usually work with the latest version of vB are ones coded for 3.5.4. Some, not all. Even then it's a long shot. Anything older is a crap shoot. Take your chances.