Great pattern for using up ball-ends and scraps of yarn. Any DK (8ply) will do.
Faces are made of felt (or suede) and embroidered, using buttons for eyes. If making for small children the eyes can be embroidered also.
I don't give tension for this pattern as it is largely unimportant. If you follow the needle/yarn type suggestion above your cat will be about 4"/10cm tall. Obviously thicker yarn/larger needles will make a bigger cat and vice versa