You'll need to figure out how many pages this thing is going to be. Generally, 750-1000 words per page is the norm, but with a monster book a lot more space is going to be taken by illustrations and margins. Calculate how much you'll pay for art, layout, graphic design, and editing. Then get printer quotes. You'll also have to budget for shipping costs, advertising, LLC set up, etc. Of course, you'll need a Web site, too, if you don't already have one.
I wouldn't suggest doing this on your own. You might want to consider submitting your idea to an existing publisher instead. You'll most likely make money that way and get your book in the hands of more people than you would doing it all yourself.
If it's under 64 pages, I'd go for a PDF. Otherwise, it's too large for most people to want to download. I don't know too much about the PDF market though.