I say do the side work and work the 40 hours a week with the company. A few things could happen such as some of the below
1. Your boss fires you
2. You realize having a business is a lot harder than it looks and have more respect for your boss.
3. You start working for yourself.
The worst case will be that People will eat you.
I worked the 40 hours a week and did the side work show for about a year. I thought This blows, Now I do something I enjoy.
Anyone that makes a profitable business deserves a tip of the hat from me.