I am almost finished writing a book myself - it is a series of romantic short stories, mostly biographical, and it will be self-published as a paperback and ebook. I am planning an audio book You should download a free copy of Audacity from the web. I reviewed it on a software hub I wrote. You will need a microphone or headset with a mic in it to record the book.
Reading it all in one go at one sitting is not easy, as the longer the book, the more tricky it becomes. The Pro's edit the different "bits" together. And Audacity will let you join multiple recording together and save them as one long audio file Audacity lets you save in a few formats. My advice here is think about the kind of MP3 you want to have. There is Lame and Blade Mp3. Blade MP3 of very high quality and takes up more space as files will be bigger, whereas Lame MP3 files has quality reduced somewhat, and more suited and okay for voice Audio book. Or you might prefer to keep it as Blade Quality.It's up to you.
Also, how do you plan to deliver the Audio book? Some DIY websites that allow free web sites to be set up - will let you download audio files but might limit the file size. So think about how people will get it or buy it. And if they are buying, then you'll need either a Google shopping cart or other shopping cart with possibly a paypal system set up. Plenty to think about. Hope that helps. Cheers!