The closest creature I can find for comparable ability scores is the grig, which is the exact same height.
Its physical scores are: Str 5, Dex 18, Con 13.
Also, the grig weighs 1 pound, so the kercpa probably can as well.
I picture the kercpa as slightly sronger and heartier than the grig, so maybe Str 6, Con 14?
For the mental stats, I see good Wis and below average Cha. Maybe Wis 12-13, Cha 8-9.
Or, to look at it a different way:
Str -6, Dex +8, Con +2, Int +0, Wis +2, Cha -2