Does Kingmaker (or any of the adventure paths) use a default point buy level? Can't find anything listed but thought I might have read it somewhere.
I believe Kingmaker assumes a standard point buy (15 points).
I use 15 personally.
I tend to think of point-buy like a difficulty setting on a computer game.
10 = hard mode
15 = normal mode
20 = easy mode
How hard do you want it on your PCs?
No point-buy system is a hard or fast rule - use what feels comfortable for you and your group. Just keep in mind that no one wants to feel outclassed by NPCs (except of course BBEGs).
We're using 20-pt because we got used to it in Society play.