Assume that the app will include a back end API and a back end data store, but that they need not necessarily be constructed with the same technology as the front end (the app on the mobile devices). By "technology", I mean programming language and/or framework and/or platform.
It Depends :)
For back end ,you need to ask are you looking for scalability ? or just fixed number of users.
What about the data base ? do you need a relational database or a non relational database .. ? if non relational ? Which type ?
Do you need to do analytics ? what type of analytics ?
For front end .. Is this an enterprise app ? Or will be used for public ?
Still I prefer to avoid cross platforms because :-
. Harder to maintain
. Lots of bugs
. Lower performance if compared to native apps
. Doesn't make full use of the hardware and OS platform if compared to native apps.
But this again depends on the complexity of the project and the target market needs. Sometimes the extra value of the native apps is not justifiable.
Again it depends.
If you need more help let me know , to discuss the case in more details to guide you the right way.