the difference between KNIME AP complete target and the KNIME AP target is the number of extensions that are installed into the KNIME AP you can start in debug mode and develop against.
KNIME AP target specifies a minimal set of extensions, very close to the default installation of KNIME AP.
KNIME AP Complete target specifies the full set of KNIME extensions provided by KNIME. It should be a save starting point for you.
KNIME AP complete internal target is meant for developers at KNIME as it references an internal update site which requires authentication.
If you have any more questions please feel free to ask them, we are happy to help you