You should supply parts. That's the only way you can control the process. It may seem reasonable to install customer-supplied parts, but that can go south quickly and waste lots of time. I learned this the hard way.
It's fine to talk about mark up and profit, but be careful. Don't expect (potential) customers to happily pay full shop rates if you're working out of thier driveway or the back of your pickup (unless it's a service truck). You need to charge for your skills, time, parts, and supplies, but it's not right to charge shop overhead and insurance unless you are actually paying for that.
Be prepared to back up what you are charging. Keep good records and be prepared to defend. Customers will challenge you before they will challenge a shop. Also expect to not get paid by some customers. They will know that you won't have the time or resources to pursue them. Depending on how you structure your business, you may not have any legal recourse.
Your customers may not always respect your availability. They may expect you work for them when you are at work at your regular job. If you're good and your reputation spreads, you can get spread very thin, very quickly. You need to make your availability very clear from the beginning.
Speaking as someone who did side work early on, it didn't work out well for me. It sounded good, but in the end, both the side work and my regular job suffered. I sucked it up and started my own business. It worked out great until the economy went south.
This is probably more than you wanted to hear.
