How to calculate server specifications for hosting ASP.Net application in company's intranet

We want to calculate the specifications of our database server and the application server for hosting our ASP.Net MVC application with SQL Server database. Roughly we are going to have maximum 300 active users per day, working in different departments. Key functions of the applications are

  1. Upload drawings (pdfs) (25 Engineering users max)
  2. View drawings (150 users)
  3. View drawing information in grids (data)
  4. download info to excel files (data)
  5. generate crystal reports of drawings
  6. update information

Information could of different types i.e. drawings, material, man power, welding, Testing etc.

Another question is: is it ok to have the database and the application hosted on the same server or there is any advantage of hosting them on two separate servers?