I've just finished writing a book that will be published by O'Reilly next year. I'd echo your comments:

1. Write an outline. This is boring, but vital. If you don't do this you won't realize that extent of the task you are taking on. By writing an outline you are convincing yourself and a publisher that you can actually write a book.

2. Do some other writing first. For example, I wrote extensively for different magazines. This is both good practice and gives you sample writing to show to a publisher.

3. "Phone a friend" Do your best to find someone you know who can introduce you either to a publisher or to an agent. This also applies to getting VC funding, it's best to find some way in via someone your know (or someone someone you know knows) than just trying to cold call.

4. If you do get a contract track carefully your progress (I used a spreadsheet) so that you stay on target.

5. Do not get hung up on the right tools to use. I've written plenty of stuff in a text buffer in emacs, or in Word, or using a specialist XML editor. Your publisher may actually ask you to use a specific tool, and the reality is that the tool is the least important part of the process. Figuring out what to write, and then writing the sentences is hard. (I'm not joking about the last part)

6. Read your work aloud. After I'd written a section I would read aloud what I'd written to see how it flowed. And I'd modify, read aloud, modify, read aloud until it seemed smooth.