Learn Italian: Questo formaggio ha un gusto amaro. - This cheese has a bitter taste.

Yes, absolutely. When talking about food, gusto and sapore both mean flavor or taste and are often completely interchangeable. Gusto is also used for personal taste, like having good taste in art or clothes.

How would I apply the da plus infinitive rule from this lesson to say the cheese is bitter to eat?

You would change the sentence so the adjective directly describes the cheese, and then add da mangiare right after it. The sentence becomes Questo formaggio è amaro da mangiare.

If I wanted to say the taste is a little bitter, where exactly would I put un po'?

You place it immediately before the adjective it modifies. The sentence would become Questo formaggio ha un gusto un po' amaro.

Is the adjective amaro related to the Italian after-dinner drinks known as amari?

Yes! An amaro is a traditional herbal liqueur drunk after a meal to help digestion. The name of the drink comes directly from this adjective because it famously has a bitter flavor.