One thing that some people overlook is the business part of a business. Most people that start shops are talented in their craft but may not have much business experience. It is good to know a little about marketing before opening the doors. Have a plan for advertising. If you don't know how...
I've had the rustoleum semi-gloss outdoors for a couple years now and it is holding up great. Use a decent primer under whatever paint you use and you'll be fine.