Depending on how far you budget goes, I would look at adding traditional cornice and pelmet and replacing the plinth with a similar oyster colour. End panels for wall units could also be replaced / added. Some chessboard style tilling in 3 colours would also bring out the walls. It's hard to tell but is the oak surround also on the wall units? I haven't checked your location but this is something we can help with

I am north facing and also in the north. Maybe our light is different here, but I have a similar (smaller) extension with one velux and it is full of light. What it doesn’t get is direct sunlight, except early on summer mornings. I also had to block up half of a floor to ceiling window in a north facing bedroom and the loss of light is minimal.

Your shelving is very cute, but maybe a bit flat. Shelving always looks better with a mixture of tall and short, fat and thin etc. Of course you are limited height wise so how about a plant or two? Say one tall and one trailing sitting on top of the Shelves. If you’re worried about caring for plants, there are some lovely faux ones about. As to lighting I think wall lights would be in keeping rather like this

I guess this will come down to how much you want to spend, if you are prepared to do an extension out the back then assume you are comfortable with some structural work. Also if you are happy to lose the garage or some of it you actually have a much larger space to work with. If it were my house and I had the budget to do a complete ‘rejig’, i would do the following: 1. Push the bathroom, utility area and storage areas into the garage but still leaving a garage door with a much smaller ‘garage’ space for stuff we just dump in the garage. Add a door if possible to the garage much closer to the front door to access the storage area. Access the bathoorm and utility via the currently under stairs door. 2. Now move the kitchen to the right into the space currently occupied by the bathroom and study, creating space for a nice size island, room fo an American fridge freezer and tall cupboards etc. 3. Move the study to the left hand side, which would run from the garden wall where the first bifolds end down to the existing vertical beam column, effecitvely making use of this as part of that study and therefore it isnt just a column in the middle of the room. 4. You will be left with a large L shaped kitchen lounge diner, where you can either choose to have a play area in front of the kitchen or tv snug and dining area to the left of it or vice versa. Whatever suits! Obviously this is without seeing the actual spaces and room dimensions to see how much open space you would get but looks like could work from your floor plan. Maybe too much work though :)