Seems odd that "ke pā" can mean "dishes," but not "dish"!
Report it. From wehewehe.org : 2. n. Dish, plate, pan; elongated food bowl used for meat or fish; flat basin; phonograph record, disk (preceded by ke). Cf. halepā.
Why is this "ke pā" and not "ka pā"? I thought "ke" was only used when the next word begins with k, a, e, o.
There is no such limit. Change your "only" to "always," and only then it becomes a true statement. But "ke" is otherwise only used with certain words, several that start with "p," for example.