Developer to create a cross platform backend system for user & data management for our iOS/Android/Windows Apps and software

We have some iOS/Android/Windows Apps/Software for industrial applications. Each App/software has its own local database to store measurement records. We are looking to create a cross platform for user and data management involving server setup, database structuring, web dashboard development, etc. Some of the requirements are: 1. Each App/software has its own backend server (we call it a module for now) on this platform for database backup/restore. If an App works on both iOS and Android, they share the same backend server. 2. There are 2 types of client accounts on the platform: company manager and staff. 3. Company manager account can create staff accounts, purchase module subscriptions and assign modules to different staff accounts. 4. All clients can sign in the system from any App/software (iOS, Android, PC, Web). 5. On iOS/Android/PC, staff account can view and backup local measurement records to online server. Staff account can also view, delete and restore his online measurement records to local database. 6. On Web App, staff account can view and delete his online measurement records on backend server. 7. Company manager account can view all records from all staff accounts under his account. 8. User accessibility to modules is based on subscription. Each module can be subscribed individually by company manager account and assigned to staff accounts 9. The system integrates subscription management. Subscription fee can be paid monthly or yearly inside the system. 10. New user has 30-day subscription trial option. 11. The system should be expandable, i.e. if we develop a new App/software, its backend server can be added to this system as a new module. Please send a proposal in doc/pdf format for this project to include: 1. Work description 2. Tasks 3. Milestones 4. Duration of each milestone 5. Deliverables for each milestone 6. Total hours and days for the project 7. Hourly rate and total cost for the project 8. Information about developers who are going to work on this project 9. Link of one of your previous projects that is most similar to this project (DO NOT send a whole page of links!) Feel free to ask any question.