Web App vs iOS App - Geo Location Considerations

I am working on developing my first app. Essentially, I am trying to create a roadmap at this point and I am having difficulty figuring out what path is the best. I need users to be able to login with either their gmail account or their facebook account. Once they log in, I need permission to access their location, pictures, name, age and interests (facebook).

Would it be wiser to develop this app for iOS and Android separately or because it is a web app, I can make it compatible with both android and iOS devices and develop it with something like jquery mobile? The location part of the application is key. I was planning on using HTML5/JavaScript Geo to look up the users current location. Will this suffice? Or do most applications use the native OS geo location tools?

Essentially the end goal is to develop a downloadable app for both iOS and Android. Which asks the users for permissions to access their friends list, location services, name, age etc. Once access is given, the user stays logged in until they manually log out. I appreciate any guidance in this regard. I am trying to avoid spending a lot of time on developing a big project on the wrong path and I appreciate any suggestions.

Thanks in advance