I'm pretty sure that all Kapok guitars are 'classical' and you should use nylon strings.

The eaisiest way to check is to see if there is a 'truss rod' running up the neck. If there isn't never use steel strings on the instrument.

Basically, shorter scale lengths = thicker strings. For 22 1/2, I'd have thought that a 'heavy' set of nylon strings tuned to standard would be fine.

Ian