A good buddy of mine (who knows a lot about these things) has always told me: Never use your own money. Use the Bank's money. I mean, I guess you have to have a little money of your own.

Why not start with an online bookstore? If you specialize in hard to find books that would be really super cool. And it would require much less overhead. I say start as a side hobby and see what happens. I've got some ideas of my own I'll be exploring soon.