Hello,
From my understanding, the app when running or in background, will let you track the users and their location in real time on your end right ?
1. We can use a mysql database for the user management part and while registering a user, can use a signup form for a email/password + deviceID (unique) OR a automated signup based just on the deviceID and a unique code. So if a user wants to or you want to identify a particular user, he can mention his 4 digit unique code. Only advantage here is that user dont need to signup manually.
2. Geolocating user on map is for your end right ? So what you will need is a simple php based backend with Google Maps integration, the mobile app will send geolocation coordinates to the database in realtime and the backend will show them on map, we can also set how often these coordinates update and if where user was seen last time when online.
3. "Users cann let others login", let others login to their account in the app ? If so, we are better off with a no-password signup and using a 4 digit code only as then "others" wont need user password to login to app.
I didnt got what you meant by "Choose Category", let me know more about it.
4. Yes, we will use mysql as the backend database and the geolocation of user will be available to you via a simple php backend on google maps (integrated)
5. My bid includes mobile app, php-REST API, mysql database setup and a simple php backend.
Regards