The difference between koukat and divat is not fully apparent to me.
"Koukat" is informal. And kind of specific to western part of the country - I myself hardly ever use it. To a beginner, I would recomend not to use it at all - "dívat" should be always fine.
Maybe it's a regionalism because of the small distance from Germany. Gucken means "to look" in German.
I am from Dresden and even pronounce it "kucken"
I think it is pretty widespread in Czech, actually. Most recent dictionaries do not consider it Common Czech so we may have to add it.
Would "Na co bys se dival" also work?
That is very unusual and harder to pronounce with the two s in sequence.