Cases of ellipted phrases?

Hi. Would you say that we can ellipt phrases like "what/that/which is" if they come after the noun they describe? Can you tell me other deletion cases like these?

Are they all correct?

Write an essay (that is?) between 500 and 700 words.

Do an activity (which is?) in the form of role-play.

Go to the hut (that is?) above in the mountain.

This school has students (who are?) aged between 10 and 16 years.

Look at the kite (that is?) high in the air.