The kiwi I was looking at is self-fertile but I think we just don't get enough sun here anyway to make a kiwi viable sadly. I think I'm going with fan-training a William pear instead (which also needs a pollinator but lots of people have pear trees, I figure I'll be OK).

You can grow a lot on a balcony. Cucumbers, grapes, tomatoes, peppers, chilles, aubergines... Any chance of pictures of yours? :o)