This is the best stand-alone arduino tutorial I've seen:http://itp.nyu.edu/physcomp/Tutorials/ArduinoBreadboard
Besides crystals and capacitors, you need a circuit to regulate power so arduino gets a constant 5V from any power source, 9V battery or ac adapter, so 3 more parts. I would not suggest you start with internal oscillator. That's just extra step that you could mess up. A crystal and a couple of capacitors aren't going to take too much space or money. If you want to commercialize your design and minimize parts, or wants to reduce frequency to save battery, you can do internal oscillator. Just snip off the external crystal and hope you understand how to use internal oscillator.