A couple things I would add to this. First is that I will never stop singing the praises of indeterminate varieties of tomatoes. If you've only got space for 2 plants but you want to harvest tomatoes for months, get indeterminate varieties, and make sure you prune them well.

Second is that particularly on a high balcony, water is going to be important to manage. The sun isn't intense in Copenhagen, but further south, the combination of sunlight, heat, and wind can dry out plants and soil very fast. My balcony (its actually a porch) isn't that high, but the sun gets pretty strong, and it gets hot. This is compounded by the fact that my porch is painted black, and you can easily feel how it is significantly warmer due to that paint. Obviously, keeping an eye on watering, or setting up irrigation (which is what I do) is a solution. Other things that are helpful are bigger pots, thicker pots (ceramics do better than thin plastic), and covering the soil with something light colored like straw.