Kuhlis need more than 10g, in my opinion. They're really energetic little guys, and if they're kept in too small of a tank, they become escape artists. They also need at least three (preferably five) in a tank to be happy. I've got three that seem to be doing well, though I will be adding more eventually.
As far as kuhlis and the
dwarf puffer, it's a chance. You'll likely never see the kuhlis, because the dwarf will keep them in hiding, but they stand a chance against it, at least, since they're incredibly fast swimmers.