A basic library, meaning not 'limited' or just 'short', but a library containing only the most important books for Hellenism, would include Homer, Plato, Aeschylus and Sophocles, then passing to the Christian era with the Cappadocian Fathers (St. Basil, St. Gregory the Theologian, St. Gregory of Nyssa), Maximus Confessor and Symeon the New Theologian, and arriving to modern times with Solomos, Cavafy, Elytis, Papatsonis and Papadiamantis.
You can use the links above to find references to specific works. However your understanding should not be determined by books only. You should also pay attention to the art of various epochs, customs, worship, etc.