Build a crossplatform app using Flutter

We need 3 fragments on home page: - One on One Chat (with expert/therapist) - Group Chat (max 15) - One on One Chat (with random people - max 10) A sound therapy page (some meditation/calm/relax/stress/focus sounds; approx 25hours audio files) A newsletter that can give them some small stories/updates (which we will write, users can like and comment) Task (so the homework that the therapist will give them to be submitted in the chat place itself, something like media options in chat but only for task/homework image) Also chat with expert is going to be certified people which will be available 4hours a day (8-12,12-4, 4-8, 8-12) And with therapists, they can talk for one hour per week session based and extra hours will cost more. We need call feature too. 4 calls per month. We want to sell this as a subscription based package instead of per session cost. So, we need payment gateway too and we'll give out all the exact details related to packages and rates and all once we proceed with the project.