How to write a business plan for an Internet startup?
puzzle-out: Your in an interesting, slightly unusual position here. That is, the investors have approached you, rather than vice versea. Business plans are normally written for a more general audience - I would find out more about these guys' other investments and see what makes them tick, and weight the business plan towards those interests. This may sound a little manipulative, but as some of the other posts have pointed out, a business plan is a fundamentally an investment-raising document, and in the medium term often has little relevance for the running of the company. 
But of course you should take a salary, it would seem unprofessional not to.