Learn Polish: Czy nastawiacie się na zapotrzebowanie, czy na brak? - Are you preparing for demand, or for a lack?

Nastawiać się means 'to set oneself up for' or 'to mentally prepare for'. Like many verbs dealing with expectation or mental focus, it requires the preposition na followed by the Accusative case.

Are zapotrzebowanie and brak actually in the Accusative case here?

Yes, they are! Zapotrzebowanie is a neuter noun, and brak is an inanimate masculine noun. For both of these groups, the Accusative form is exactly the same as the Nominative dictionary form.

Could I use przygotowywać się instead of nastawiać się?

You could, but it changes the nuance. Nastawiać się emphasizes a mental attitude, mindset, or expectation. Przygotowywać się is more general and often implies taking concrete, practical steps to get ready.

Why is the word czy used twice in this question?

The first czy is the standard question particle that introduces a yes/no question. The second czy means 'or'. When asking a direct question that offers alternative choices, Polish uses czy for 'or' instead of albo.