Everybody seems to want to start a computer repair business these days (myself included)...heh.
Here's a little something I wrote about it.

One thing you should keep in mind (maybe you are, but I definitely don't see anyone mention it): the legality of your business.
Make sure you've got properly written contracts, that you cover yourself in case something goes wrong,... and don't get in trouble with the IRS

A little example: make sure you know the (dis)advantages there are to the different business structures. Going with a sole proprietorship is the easiest option, but keep in mind that if you ever get in debt (and that risk is real in sue-happy America), creditors may go after your personal assets for satisfaction of debts. If you go with another option, you're facing a stack of paperwork...