I like to start with nuget because it handles setting up all of my project references. I create a new MVC4 Web Application
Visual Studio->File->New->Project->MVC4 Web Application
After I create the new application, I open the Nuget Package Manager Console
Tools->NuGet Package Manager->Package Manager Console
I then enter the command:
Install-Package UmbracoCms.Core -Version 7.2.1
I find that installing the UmbracoCms.Core instead of the whole UmbracoCms nuget package is best because it only sets me up with the umbraco dlls and sets up the references for me. The UmbracoCms nuget package tries to do a lot more and is more handy if you are setting up a brand new umbraco site in Visual Studio.
Once I have nugetted the appropriate version of umbraco, I copy my existing umbraco site files over the files that were nugetted. When you copy all of the files over, don't copy all of the App_Data. Most of the files in that directory are TEMP files and cache files. From App_Data, only copy the following. This will save you time reindexing the site. I suspect a lot of the App_Data files were responsible for your Object Null Reference.
App_Data/access.config
App_Data/packages/*
In visual studio, in the solution explorer, click "Show All Files", and then include the appropriate files in the solution. Rebuild the solution, and you should be set up for development.