Is việc này required here?
well yes and no. you need either that or an equivalent (cái này, điều này, etc.) -- it could virtually be any classifiers (except maybe classifiers denoting a person or an animal) + này, depending on what this refers to.
Note...also accepts 'kể với chúng tôi'
It seems to me that nói just means make a sound where as kể has a more of a 'to inform' tone
should have more answer for this quenstion
Cho should be optional, reported.
there would be sthg missing if you take "cho" out. the flow is kinda broken.
what makes you think that it should be optional? you have to be really sure of yourself when you do such statements.
Well then it should be taught that way, as it is not presented like that in other parts of the lesson, and the hint doesn't include cho.
do you want to learn how VNmese actually speak or you just want to construct English sentences with VNmese words? if the only thing that bugs you is hints, then I'll just change it.