I'm not entirely sure self-publishing is the route that's right for me. I can't network for the life of me; in real life or online. The most I could realistically achieve self-publishing is the personal satisfaction of a screen shot of my book on Amazon.
That said, I keep reading about it.
As I understand it, a print book (such as a POD from CreateSpace, to keep this about self-publishing) has one ISBN, and an ebook (Kindle/Nook) requires another, and any other form of the book would require yet another (an audio version, for example, would need a need a separate ISBN number). Kindle, Nook, CreateSpace, all provide ISBN numbers, but they also retain a percentage of the sales.
In Canada, a writer can get an ISBN number for free; Canadian authors simply need to register with the government as a publisher. (You can apply for one or a sequence of ISBNs - they ask how many books you think you'll publish in a year.)
Canadian authors with marketing and networking skills can get 100% of their sales by registering as a publisher. Nifty to know!