Quick answer on this one: talk with somebody who has already succeeded in this field (built similar product or company). He/she will be able to quickly get you on track and avoid common pitfalls of your industry. If this person can't help you 100%, he/she will certainly be able to point you other...
In the realm of custom work, fixed prices are dangerous ground. It puts you in a position to either say "no" or ask for more money when a project has extra needs, and that's never a comfortable situation to be in. You said yourself that speaking to a lead is the best way to make a sale. I'd ech...