I don't want to dissuade you from getting another duck and generally I'm all for it because I believe they should have a flock. However, in your situation it sounds like it's not an optimal environment for even one duck since you mentioned it would be on the balcony.
We've seen a similar situation unfold on BYC.
I'm not sure why you decided to incubate eggs.

If the one does hatch, I would set it up with a mirror and a stuffed animal until you rehome it to the farm. Hopefully that happens sooner rather than later. However, they do cry a lot when left alone. Singletons also tend to cry a lot at night. So, I hope you're ready for it to be totally dependent on you.
I saw that! I do hope it hatches since you've worked so hard.