Are these correct?

Malu is a kind of Maori cracker
Malu is a kind of Maori crackers
Apple is a kind of fruit?
Apple is a kind of fruits?

Does a plural follow after "kind of"

Then
I'm wondering if I have to pluralize the noun.

Apples are a kind of fruit?
Apples are kinds of fruit?
Apples are kinds of fruits?

If I don't use kind of and just say

Malu is a Maori cracker. Is this ok too?

If I want to say Malu is delicious, using a pronoun

Should I say
They are delicious or It's delicious.
Malu does have an s so should it be singluar


thank you