I am confused whether I'll need to add columns/walls or not. As you see, it is possible, but without them it would look much more realistic. I think.
There are two distinct steps when creating balconies:
1. Actually creating your balcony. Here you will
have to add either columns or walls. If you don't, you aren't able to put floortiles on your second story. This is the phase where you actually create the balcony, so floors, fences, all the building elements that need to be supported to create.
2. Once you created a balcony, you can choose any option you want. You see, once that flooring and those fences are created, you are able to delete all elements you
needed in Step 1 to create them. This means that you can create a balcony that's completely unsupported. However, if you want, you can also keep a few columns, or a wall, anything goes. Step 2 is where you design the balcony just the way you want it to be.
I hope this cleared it up a bit. There's a very big different between what you need to create a balcony, and what you ultimately have to keep to keep your balcony hanging (basically nothing, you could even let it float in the air). When you then talk about realism, you're only looking at Step 2. If my balcony is this big, does it look better with or without support. But you don't
need anything after Step 1, so you are free to make any choice you like.
