The thing with asking such a question is you will get a lot of good suggestions - which is great - but I would compile a list of things you want from "your" garden. eg.. How much time will you spend in it?... will you actually do any "gardening"?Do you want to entertain or will it be a private space you can relax in?Will it be used by pets or kids?What style of garden do you like?Whats your budget?Give yourself 6 to 8 months to think about what you'd prefer.. have a walk around the local area to see what grows well & perhaps talk to neighbours with established gardens?In that time note how wet or dry it becomes & see where the light falls.I would be chomping at the bit to get going too but try and resist so whatever you decide wont disappoint you later on (or waste time & money).
I would deep some deep holes and see what the ground is made of - if you have much topsoil, how it drains. The nature of the ground may well determine what you do with it.
You will have a lot of soil improvement to do in the future...amazing how the developers are allowed to do this. It's not a sustainable depth for long-term gardening.
the enduring gardener said:
I'm prefer to draw than write so I did a sketch (a very rough one) based on your pictures. I think a couple of circular lawns will add some structure to the space and give you plenty of space around them for planting. I've put the office in the closest corner through a rose arch which will keep the space open in the larger part of the garden which has better views beyond. A birdbath or bird table outside the window of the office will be a welcome distraction. In the other corner there's space for a focal point - maybe a pergola with a bench beneath ? The fences here would be lend themselves well for training a couple of fruit trees up. Between the lawns there's a small pond to keep the wildlife happy and give you something to look at from the house. It's all very exciting and you'll make it your own but hopefully there's a couple of ideas here that will get you thinking. Best of luck.