Web app plus Mobile app hosting server : how much juicy it needs to be

Here is some information regarding the app.

- The app will support mobile version (iPhone and Android) and web version (website).
- In 6 months target audience is 10,000 users
- It's a social networking app (I guess, this increases number of hits compared to other apps)

1) Should we have dedicated server or shared server?
2) How much bandwidth is required? 2TB etc
2) What type of processor is required (dual, quad, hex etc.)?
3) How much RAM?
4) Managed backup and RAID and this kind of stuff?

How should I decide?

Run load tests.

Thanks Peter, it was more for budgeting purpose as I was looking for hosting cost. App is not developed yet.