For International Music Festival Artists

IMPORTANT: READ THIS FIRST!
As an International Artist (from countries other than Canada), do I need a visa to perform at the SXSW Music Festival?
As an International Artist from Canada do I need a visa to perform at the SXSW Music Festival?
As an International Artist supported by an export office, funding body or other entity, do I need a certain visa type to perform at the SXSW Music Festival?
As an International Artist, when should I start the visa process?
As an International Artist, how do I obtain a Support Letter and/or Entry Letter from SXSW?
Should I notify SXSW if I plan to showcase at SXSW and am using the VWP or have obtained a visa?
Should I notify SXSW if I am at the U.S. port but denied entry into the U.S.?