Indeterminate greenhouse tomatoes or parthenocarpic cucumbers (Lebanese types) can succeed during the late spring, to early fall. This is when the light levels are strong enough that even indirect light is enough. Squash not so much. If you could get some of the winter varieties grown in the greenhouses in southern Spain, maybe.

All of the leafy greens are possible year round - lettuce, spinach, kale, etc.

For some permanent greenery houseplants are an excellent choice. Ferns, african violets, mosteras, philodendrons, kalanchoe, etc would all do well in that spot. Sydney very rarely frosts so you have a wide choice to choose from. Pretty much everything will work. For watering make sure you good drainage on the pots on only water they are dry.