Assume you had access to a 6 by 6 balcony that faces south with a nice railing and (miraculously) endless access to water. Set whatever budget makes it interesting for you. How would you design your garden to produce as much food as possible? Could you produce enough to sustain yourself? How close could you get? What crops would you prioritize?
If you have limited space, quality compost ensures you get the most bang for your buck, it makes a huge difference. The best results I’ve had have been for potatoes, peppers, tomato, radish and the best compost was from our community composting bin (yes, made from our pooled veg scraps).