The problem you describe does not require a complex technology stack.

Front-end: HTML5, sure. Considered JQueryMobile for the mobile app?

App: Use whatever you're most comfortable/experienced with. Even if that's PHP, use it.

Database: Have you been looking at MongoDB specifically because of its good geo-spatial indexing? If so, that makes sense. But if you don't need it - just use MySQL/Postgres. You'll be able to reach your goal without the learning curve of using a NoSQL DB.