Android App Development Considerations

Hi All,

We are new to app development so looking for feedback from the community. Some of the questions may be stupid so please bear with us. We are planning to build an application that will be highly data intensive and used by large number of users simultaneously (hopefully).
Questions.
1. Is it always better to build native application or cross platform development frameworks like Xamarin works pretty good as well. We have limited budget to trying to reach as large customer base as possible before we have enough budget to build individual platform native apps. Thoughts!
2. What % of people in US and world wide use android based devices (so we can figure what platform to first build for)
3. Are there back end architecture available for highly data intensive and scalable apps that someone can point to so we can use that as reference as we are building the app.
4. Any other gotchas or considerations we can keep on mind as we build our application based on your own experiences.
thank you for your feedback!
AJ