I've always wondered how the biggest apps out there, that sometimes start with little to no funding, become so huge and get so many adopters (like Snapchat). If you've been successful in that space and had to do it all over again: which platforms, strategies, forums, etc. would you launch on to get early adoption and then mass appeal? It's very hard for me to understand how to execute and get a clear path, there's just so many things to do at once, that you can become scattered.
If you are solving a big problem through your startup then people will love you and will definitely use your app. Necessity is the mother of invention and failure is the mother of success. So don't be afraid to fail, just build it and present it to the consumers.
For a massive launch, you have to do Growth Hacking. It's a combination of engineering and marketing. This is the practice that is common in leading startups for the app launch.
I am sure, I can help you if you wish to setup a call. I am an expert with multiple skills :)
My best wishes.