If you can swing it, don't overlook the 550d. It does very well as at widefield shots, DSOs, and has the added benefit of Movie Crop Mode which you can use for planetary imaging. The 18-55-IS lens is a nice little lens, and despite being a little slow, it's definitely enough to get you going.

The cool part is, if you end up upgrading your mount and getting a scope, it's versatile enough to where you don't need another camera to learn the basics of a different type of AP.

It also does HD movies and is a nice daytime cam.

There are a lot of lenses worth buying. The 50mm 1.8 is cheap, fast, and tack-sharp. I'd definitely recommend that one. All the other lenses I want are pretty expensive. For widefield/milky way shots, a lot of people seem to be using the Rokinon 14mm which seems like a lot of lens for the money. Haven't tried it out personally, but it gets good reviews.