Add features to an existing Flutter App

I have Flutter App that is already published in both AppStore and Google play called "Jahhiz". Jahhiz is a food ordering application where you want to order food to be Processed for Pickup only, or for Dine-in (eating in restaurant). It is not a delivery app. The tasks are: 1: We need a menu for each restaurant. A menu where restaurants can add their meals and categories. So that a customer can view the restaurant's menu and select how many of each meal. 2: HyperPay (payment gateway) integration. We already done 50%-60% of the work in Node.js what's left only the last step where the payment gets processed. (I dont mind if you want to re-do the whole thing again.) 3: Push Notification with Chosen Ringtone (either custom or phone-specific ringtones). We are using Firebase so it'll be simpler. 2 types of Notifications: 1- For alerting restaurants and customers of their order status. 2- Advertisement notifications other minor changes: - A restaurant can manually set availability to Open/Closed. - Before sending out the Order request, a customer should set how many attending the restaurant for "Dine-in"/"Local" ordering type. The default value is 1. - Easy fill-in of the verification code from SMS msg. By one click. - Vendors can refuse and accept orders. - Financial Report generation on the fly for any Restaurant Sales. These reports are sent as Email, and generated on the fly. The generation of this report, will require the restaurant to manually input dates "FROM" and "TO" to be generated in this time frame. MUST: - Sign an NDA. - Use Github private repository. - Use trello to update. - Time is crucial, we want this up and running asap.