MongoDB will be just fine, i suggest using PostgreSQL for the relational database (if needed) PostgreSQl offers better stats for handling great amounts of data.
Based on the website https://www.techempower.com/benchmarks/#section=data-r10&hw=ec2&test=query
we assume that the best choice to run services will be JAVA (specifically undertow) this will give a boost in answer speed and calculations, even over the technologies already proposed by you, if needed we can always use the proposed ones.
Back-end can be developed solely by web services or through TCP/IP protocol using sockets, messages will be handled (line system) through JSON.
We can (optionally) also add GPS devices support to the platform, this will allow vehicle control (if needed), options like turning off remotely, locking and unlocking the doors; setting maximum speed alerts and geofences.
The system will count with float management in users modules, with which you can supervise and do the previously described actions. this feature will only be available from the web page while the client can only access so many features from the mobile app or web.
The structure will be as scalable as you wish, this will allow user management and role creation to distribute the over viewing of the vehicles.
For more details about what we'll be able to provide you, contact us free of charge. We can Re-Design the proposal to your convenience.