How to validate a startup idea?

I want to make a roguh model for validating startup ideas. I want some help.

Here are some of questions which come to my mind? 1. Where will the revenue come from? 2. How many users are required to get this revenue? 3. How to get user to use the product / service? 4. Is the product / service and absolute must, something which users cannot do without? ...

Can you add more or give me pointer to information?