You're right about "development" part, especially for the initial feature set. I do consulting, and I estimate efforts for initial development vs maintainance as 5% : 95%. If you aim at millions of users, probably it should be 1% : 99%. It might be easy to find or replace somebody who does that first 5% or 1%. It will be difficult to find somebody who has commitment to hang on for the rest of 95% to 99%.