Not trying to be negative, but well sorry, I see red flags.
1. You start by saying 4 10 hour days do not leave you much free time.
I own a shop, and if I worked 4 10 hour days, I would consider myself to be on vacation.
You need to evaluate your desire to do this and must have a passion for it other than, "I could not find the job I want". You must be prepared to work 7 days a week 14 hours a day. If you are not prepared to do that you will fail.
I have seen it time and again- sorry, just the facts.
2. When starting a business most banks will not even validate the concept of the business being any sort of separate entity for a minimum of 2 years.
Until then, you are the business and so is your credit.
If you can get past these issues, and I think you can if you have the desire, put together some sort of plan first, i.e. the only answer to your question on how to quote is going to come from people in your area. How I quote or anyone else quotes is irrelevant to your situation. You must compare and benchmark to those you will compete against and find out if you can compete and still make money.
Hope that helps, not trying to be negative, but don't get involved in something you are not going to be happy with. Its not as easy as changing jobs if you find yourself not happy...