Requirements for creating an HTML5/Mobile App

I am planning out this project for research purposes. The basic idea is to build an HTML5 app similar to Foursquare; users can connect, select some interests, and nearby people with similar interests are displayed on a map. The focus is for the app to be highly scalable. I have almost no experience with web development, I have only ever created an ASP.NET website.

From my online research I think that I can achieve this project using the following technologies:

• HTML5 with ASP.NET and MVC for the client and server side code
• MongoDB for the backend database
• Websockets for realtime communication (or web services?)

Will these technologies be sufficient for my project? Have I left something out of my considerations? Are there other tools/technologies that you recommend?
Any ideas are welcome, as my greatest difficulty so far has been just analysing the different possibilities. Thanks.