The team working on this must understand that quality is extremely important. Please no time wasters. You are familiar with WeChat, KakaoTalk, Whatsapp , viber etc... Quality should be similar to those and on top of that, we will need to add extrea features. Will explain in private, however please, you need to be fully experienced, know what quality means, and understand the needs here. Do not bid on this project just because it is an available project, please read before. Also i will ask to see a portfolio of apps you've done similar to chat apps.
Of course a presentation website will be needed also to present the app with a video and addtional info.