Selling a website idea: What to expect

I created an idea for a website that has gained the interest of a private investor with deep pockets. He wants to pour a lot of money into the site and hire me to front the project for the time being.

Note that it's just a business plan at this point -- no actual product. That will be developed in the first six months.

He has offered me a percentage of the shares of the company and a reasonable wage. I have no idea if what he is offering is standard, generous, or if I'm being taken advantage of.

I'm going to hire a lawyer, but I don't know what kind of lawyer to hire.

Can anyone help give me an idea of what I should expect, of how these deals usually divide up between the idea guy/developer and the business man?

Thanks in advance, and Happy Thanksgiving!