For catfish, personally I would avoid mono or fluorocarbon hooklinks, and go to coated or plain braid, although plain braid will get plucked.
Length I would probably look at 150-200mm long for rigs, with around 20mm from hook to bait on hair.
Bait for cats is fairly simple, 20mm pellets, 2 or 3 on the hair, gives you a chance of both species, as will any fishmeal boilie.