Bring the window down to meet the cupboard. Really lefty47 was right about not drawing attention to it. It is a source of light ,,, so no need to clutter it up. But if you took the colour out and painted the top of the cupbard to match the wall it ceases to draw attention to itself. Just because it is a horizontal space does not meant it needs something put on it. Note- With the cupboard being white, it also draws attention to itself … perhaps take that to the wall colour too and lift the pendant a smidge. So your pendant is the feature there. The cupboard … do yo need it? One way to remove what you are calling dead space is to get rid of the cupboard.

Well that is an interesting picture. I can assure you that hanging wall gardens are all the rage and that is a great idea but they can also be high maintenance if exposed to high winds / sunshine etc. I have seen some lovely fake ones that would do just as well. You could also have a few pots with additional greenery. As you say your view is not "great" maybe you can have a creeper in one of the pots that can weave its way through the railing. I probably wouldn't go for one big chair as it could dominate the entire space. I would consider a table with a couple of fold-able chairs .... something that is comfortable, inviting if you have friends over but can be placed in a corner if you just want to open up the space. I do not think you need a carpet and but maybe some fancy outdoor tiles will look just as nice. You want it to be easy care and weather proof. Do you need or wish to incorporate a washing line? A pull out one from a wall will be perfect that way you can retract it back when you are not using it. If you deck gets too much sun, you may want to consider some shade shutters. I have seen them called 'plantation' shutters. GOOD LUCK

I would consider a small retaining wall perhaps 2-3 planks high this will provide support to the bank but also allow the pathway to remain clear and formal. The ferns seem to be doing well but could do with a tidy up. I would also prune the tree so it allows a bit more light into the section to help prevent dampness, you also want to take it away from the house, without destroying it's natural shape. As ferns seem to naturally want to grow there, you could continue that theme. Perhaps some other shade / cooler temperature type plants with some flowers could be a good addition. I am not sure which plants can tolerate the cold Dunedin winters, so you best contact is your local garden centre. You want plants that are lush all year round. Also have a look at other plants growing in the neighbourhood as that will give you a good idea of what does and doesn't do well in your climate. Good Luck.

We have very similar narrow side gardens. Judging from your picture, I'm guessing that you get more sun on the left. So, close to the door you could have pots of varying sizes and similar colour with dark leaf cannas and contrasting agaves potted, which won't overtake your garden because of the pot restriction. On the shade side, I'd plant ferns at intervals with clivia inbetween. You could also put up some chicken wire on the fence and train jasmine. On the sunny side, cordyline show-off, vireya rhodos, hibiscus (beautiful varieties) and bromeliads for groundcover. Good luck and have fun.