I think its cool you want to learn more about cats. Not lame at all. I'm sure there's a ton of stuff I don't know about dogs...and I used to be a "dog person".

Here's a website of a local SPCA: http://www.sspca.org/CatBehavior.html

I learned about cats by reading one of those "Big Book of Cats" books. It detailed everything you're asking about...why they do things.

I'll say that when cats are vocal when they play, its probably just how they're playing. I know when Noah and Noel and when Sami and Phoebe played...and even Hermie and Basie too...they'd make differing meows based on HOW they were playing.

Wagging of their tail CAN mean more than one thing. They wag when they're interested, annoyed, about to pounce, etc. They're like people and are different.

You're correct on the open mouth thing, they do that after they smell something different. Opening their mouth further enables them to smell more.

Hope you learn a lot! Have fun!