Beast,
Freight is a very vast and varied operation with everything from single pilot short haul ops to multicrew long haul international. It is far less glamorous than passenger flying and a huge percentage of freight operations take place at night. The requirements can technically be as low as just a CPL, but of course then you cannot fly in controlled airspace and are of no use to a potential employer.
Multi crew operations obviously need fATPL, but I do not know what the single pilot requirements are, I susoect that may well depend on the operator's insurance. The freightdogs forum would probably be able to offer more information.
Regards
Obscop