There is no easy and simple answer to this question. It depends on many factors the not least how much risk you are prepared to take and more importantly how much investors are prepared to lend and risk with you. The solid business plan is the basis for deciding that and can produce the cash flow analysis.
And always remember……………The wise words of Adam Smith …..
“It is not the benevolence of the butcher, the brewer and the baker, that we expect our dinner, but their regard of their own self interest. We address ourselves not to their humanity but to their self love, and never talk to them of our own necessities but of their advantages”