I never did like working by the hour. I always felt I couldn't work hard enough to earn the money and would work myself to a frazzle. When I decided to go into business, I made my self a couple promises:
1. I'd always supply my own materials so I could control the quailty.
2. I'd always make detailed proposals, so everyone would still be friends when the job was finished.
3. I'd always work for a contract price and never by the hour.
4. Always a detailed contract, even with friends. It keeps you friends.
5. Always preform work in a way that if anyone ever said anything bad about me, they would have to tell a d&*n lie.
Starting out, sure I missed it on some jobs and didn't make much money (Still do sometimes). But, I never went hungry and the bills are paid.
As to price per sq. ft. You may have to start out a bit less than the going rates, in order to get some steady clients. But remember, you owe it to all painters to raise your prices as soon as you feel comfortable. We all win in the long run.