The course that's linked in this post is excellent for the price. Pretty much all of the engine stuff carries over to motorcycles. Everything else I pretty much learned by looking up specific instructions for my model along the way, either on Youtube or in the service manual for my bike.

As for what bike might be interesting, I bought a fuel injected, single cylinder bike. Pretty much as simple as it gets, and a great way to get started with the basics.

Don't be afraid to jump in, you'll be surprised at how easy it comes to you.