If I'm buying BTS, do I need Warlords first? Does BTS include all of the differences that Warlords brought?

No, you don't need Warlords to install or run BtS.

Yes, BtS includes the game play changes that were introduced in Warlords, but you don't get the scenarios that shipped with Warlords.

I'll add this Q & A to the FAQ thread.

Okay, thanks. I don't play scenarios anyway.