I've been into computer and electronics since I was a a pre-teen. It's something that I applaud you doing but don't think of it as a career. I've worked 25 years now as a senior electronics tech doing component level repair and I can't even with my own family keep up with the machines I have to refurbish anymore.

I wish you the best of the endeavor and am sure you will get lots of clients. Be fair, be honest, etc and you will profit a bit and make people happy.

If I can offer any help just ask.

FYI some parts places to find old/obsolete electronic IC etc stuff:

www.jameco.com
www.newark.com
www.mouser.com

Designate your workshop or a room of your house for the business. You can then write off part of your mortgage as a business expense.