Flutter (or Android and iOS) App Development

We are a small team working to develop an app for live concerts and corporate events. We have made some one-off working demos, but don’t possess the skill set to develop apps for production-scale. We have parttented IP we are looking to develop into a cross-platform app with Flutter or some other platform/BaaS. Ideally, the application is written in Dart/Flutter, and would require minor back-end development with Firebase and some UI development as well. for the skill set, we need somebody with UI development experience, ideally someone who is familiar with NTP (Network time Protocol), and someone who is comfortable developing cross-platform.