Simple progressive web app

Simple but well-built progressive web app that shows a nice header picture and says "we are launching soon". It presents users the option to sign up (name, phone, email, location, etc.) on the home page under various categories (buyer, seller, etc.) and create/modify their account. Users should be able to add app to home screen by tapping "add to home screen" banner at the bottom of the screen. On the back-end, the key functionalities required are: - data monitoring and analysis module: admin should be able to filter and view data (signups, adds to home screen, etc.) on graphs and maps (e.g. markers shown on a map for each signup for selected city) - user communication module: admin should be able to create "conditional campaigns" to bulk send registered users messages/notifications - user management module: admin should be able to define user categories (buyers, sellers, etc.) and the signup criteria for each (seller may need to upload documents, for example) - admin should be able to download/backup data Recommended stack is Firebase with React, but open to ideas. Development objectives are: - Modular development so that new features can be added separately and old features can be modified easily - Lowest possible development cost (stack related costs) - Cheap running costs (server, etc) - Quickest development time (incremental development vs building every iteration from scratch)