Best Practices for Developing with Sitefinity

Hi -

 We are evaluating sitefinity as a replacment for Sitecore (another .NET CMS).

 Can someone help me understand how it is best to develop with Sitefinity and Visual Studio?

 I would like to be able to create widgets, themes and all other elements that are necessary for a site.

  With Sitecore you opened up the folder containing the website and started working from their.

  It appears with Thunder I can create a Visual Studio project for themes.     Do I need a separate Visual Studio project for the code assets (widgets, controls, etc)?

  Is it a good idea to  open the folder containing the Sitefinity site in Visual Studio as a web site and start working from their?

  To me it makes sense to have one Visual Studio project where all your assets could be maintained.     By assets I mean themes, widgets, controls, etc.  

  I can't seem to find any good documentation on this discussion.

 Thanks