yes, because it's an "introductory clause," so I certainly would put one there. But no comma before "which." I'd say "that" there instead, too.

Vergl. mit: related discussion: Later,... Moreover,... etc. mit oder ohne Komma? . . .

danke!

Moreover, there are ...

The word 'moreover' is an adverb, so you need one comma for it, plus one for the clause.

It seems a little strange here, maybe redundant with 'also.' Usually you don't use 'moreover' when you're listing categories, but when you're giving an additional example or making an additional point about something in the same category. It might be better just to say

Another category is moral books, which try to teach children a lesson.