At the moment I am trying to get into the ASP.NET MVC framework.
For most of my test applications I used a single assembly/project. This worked fine for some smaller app
Only completing @David's answer:
If your project is managed by NuGet, after creating the class libraries, perform a copy of your packages.config file to the class libraries root. Afterwards, you should edit each packages.config file adding or removing packages, according to the needs of each class library.