Always User Journeys First!
Developers want to help but their priority will always be winning the job. Knowing enough to get good estimates will keep you from overcommitting or starting an app that won't be financially viable.
Developers will welcome well defined user journeys!
Don't contact any developers until you have your User Journeys nailed down!
An app without a commercial model is just like my needy, disabled rabbit - it might look awesome but it will take all your cash to keep it alive. TechStartSMART
If your app has been designed to solve a specific problem, your ideal users will be happy to give you money to get the solution. TechStartSMART