Take what time you need to plan things out. Waiting a week or a month extra with launch is worth it if it means the RP will survive longer.

Oh, and get a good co-GM or two to help you plot things, or at least someone to discuss (or argue) with. That'll help find flaws you yourself won't easily spot.

Don't be afraid to start an RP over. Sometimes, flaws that snuck in during planning cannot be solved any other way. Its better for all to start it over as a new version than to keep going with something broken.