Android App - Cloud Data - Offline capabilities - Gis related - Multi user / multi entity

I want to manage workers that go to a working point and execute some tasks. I want to control the amount of time needed to arrive to the destination, the job done, and manage pics associated with the work done. I also want to start recording travel times to optimize the workers routes, as they are actually a bit random.

Thus, I need an estimation to create an (android) app to do the following:
- admins can create tasks, create working points with associated data, and assign task+working point to a user in a given date.
- The user will download the assigned tasks of the day for one or many working points from a centralised (cloud) database
- the user can download data related to his tasks, such as Google Map location, or open QField working point location. GIS data will be treated apart in the QField app.
- The user does the work and fills a form related to his job, and uploads pictures to show job done and/or incidents. The app should be able to work off-line as often there are no connectivity available in some of the working points.
- App tracks the device, so the admin can see in RT where each user is. Also app has to register arrival time automatically to avoid users cheating
- all these location data will be stored in the cloud, so that they can be exploited in a later phase, to optimize working routes, etc

Price of the work includes source code. You provide the source-code and we compile it.
Previous experience in similar programs is a plus.