OK, if you're serious about starting a buisness, first thing you want to do is find the nearest SBA (Small Buisness Administration) office, or go on the web to
http://www.sba.gov . Go there, find out all you can about home/part time buisnesses. There are tax implications (extra deductions for using home space as an office), insurance (homeowner's may not cover an accident in your basement if it's work related). Find someone to talk to, ask lots of questions.
Next, you'll want to do field research. Call other repair shops, see what they're charging, want kind of warrnaty they put on their work. That'll give you a range to price at.
Finally, you'll need money. Advertising costs. So does setting up a company (even a partnership, part time). You can ask at the SBA office, but you might want to consider how you're going to pay for parts you need, how you're going to pay people for their work, etc...
Just a few thoughts, as I file my incorporation papers myself.