It's good that you know what you want, but I expect that here you will be constrained by the market. I've been involved in startups a long time, and I have honestly never of a developer who is not only being asked to work for no salary, but to buy in with cash. You may see it as "giving away equity for nothing", but they're going to see it as payment for work. "Please pay me so I'll let you work for free on my business that, as far as you know, will probably fail" is not a particularly appealing pitch to anybody who can turn around and easily get a solid salary.

Instead of buying in, the typical way this is handled, at least in Silicon Valley, is to adjust the amount of equity. The more value they bring, the more equity they get. The more valuable the company is right now, the less. The lower the salary, the higher the equity. Whatever relevant factors get rolled up into a single number.

Yes, you'll definitely want vesting. Hereabouts 4 years is pretty typical. For people joining later, a 1-year cliff is typical. But if they are coming in early and aren't getting salary, then I think it's normal to start vesting right away.

As to the actual amount of equity, there's really no guide for this. If you're before both investment and revenue, there's little objective data to say what the equity is worth. You can see noted venture capitalist Fred Wilson talk more about that here:

http://avc.com/2010/11/employee-equity-how-much/

I haven't watched it, but he also did a live class on the topic here:

http://new.livestream.com/Skillsharelive/MBAMondays/