Just be aware, the App Engine is not a great choice for every project. Simple things are really easy, but moderately difficult things are damn near impossible. But it's a good way to get started.
Don't let that put you off though. You need to learn a heap to do web dev, and anything that cuts down the initial complexity is a boon.
They purposely force you to write google-scale code, which isn't necessary for an early stage startup. If you hit the ceiling of what you can do easily, you will have to switch to django, or do some hardcore appengine stuff - don't write too many relations, just denormalize. Want to keep a counter? Bad idea, use sharding. Want to sum up a database column? They advise you to use map-reduce. It's all good advice for a super-scale app, but you probably don't need it.