How would I suppress all warnings (or at least as many as possible since those prefixed with MSB cannot be suppressed How to suppress specific MSBuild warning)?
The best way is to fix the issues that are causing the warnings.
If you must ignore the warnings (e.g. you have inherited a project with so many that you can't see the wood for the trees), you could try changing the WarningLevel property, http://msdn.microsoft.com/en-us/library/13b90fz7.aspx