The first few walkthroughs here go though how to create sprites - the most basic thing in Unity
http://unikronsoftware.com/2dtoolkit/doc/Aren't background just a bunch of sprites arranged in the way you need?
You do need to know some basics of using Unity before using 2D Toolkit. The component based architecture is very different to other engines, and that in itself is a much bigger "jump" than 3d -> 2d in my opinion. You're definitely not wasting your time with that Game Dev Essentials book, it goes through and covers a lot of the core features in Unity. Building a 2D game in Unity is just like building a 3D game in Unity, except its displayed in 2D - none of the stuff you learn will actually go to waste.
I'm working on a bunch of tutorials that go through building a simple bug squashing game from start to end, with a basic and functional start and difficulty selection screen. It expects you to know how to do basic things in Unity, though, for example navigating the scene view, how it relates to the hierarchy view, the distinction between the project & hierarchy windows and so on.