mobile app similar to tiktok and insta with AWS backend

Build a mobile app that
-Captures video, photo, and audio contents via the app using phone’s camera and microphone
-play them back as needed in an efficient way inside the App - in the same device as well in other devices
-The audio and video files are not stored in the phone; they would be stored in S3 and retrieved from there for fast playback
Screens to be built:
User signup/login screen - integration with Amazon Cognito; Cognito component is being built separately
Four additional screens around capturing and managing the contents
App in both IOS and Android, and a website
App built in React Native/ Flatter - should integrate seamlessly with AWS backend which has been already built( APIs)
Wireframes, screen flows, and API details will be provided in form of a technical specification
Backend high level details( already built):
Serverless backend: - AWS API gateway -> AWS Lambda -> DynamoDb
Content stored in S3

Trying to get relevant quotes from competent freelancers who can build the app and can integrate with AWS backend that I am building separately... will share wireframes, tech specs, and API details once the preliminary screening is complete and NDA is signed...

please share your expertise, previous work details, and ask questions...

thanks.