I've just come out of the SharePoint world and whilst I'm now in a Java world I've setup a solo boot-strapped micro ISV to cash in on the knowledge that I still have.
The only thing I'd add to that list is that if you're doing anything with the Microsoft stack then you should go and sign up to BizSpark. It will give you all of your software (dev tools, test stack, etc) for free which will help reduce an initial overhead.
That takes time, so do it immediately after 15. and 25.
BTW: I'm already making £3k per month from this and so far I've only sold a few WebParts to existing contacts. I would totally recommend little side projects like this if you do have specialised domain knowledge that you can take advantage of in a way that doesn't conflict with your current employer (if you have one).
The motivation to start the micro ISV was simply to fund my MSc and to cover the costs of the hardware that my project/paper requires. But it's quickly becoming a viable business on it's own so I might keep it up long-term.