I understand your impatience BUT it's easy and expensive to make mistakes ( garden centres are full of people who have made mistakes and are buying new plants!)
I'd do nothing between now and the spring except plan it.
You need to see how the sun shines on it, where the wind tends to come etc.
I'd probably plant some trees- maybe fruit trees or evergreens at the back to screen those outbuildings (assume they are yours- back, far right?)
I'd want some fencing, either living as in a hedge or tall shrubs, along the drive where you have your rotary clothes line so it looks more like a garden and not just lawn leading onto tarmac. Maybe a beech hedge or lavender, or even privet.
I'd forget about doing much to the 'sunken' bit unless you want to spend a lot- it either needs a load of earth so it's as high as the lawned area beyond it, or you could terrace it with sleepers or something. That will cost.
To be honest, it would be better if you posted more photos to see it from different angles. If the 'sunken' garden is outside your back door, how do you want to use it? For sitting out? For vegetables? As a huge rockery?
And other issues- do you have young children? Is the terracing an issue? Do they need a play area like a lawn? Do you want mainly flower borders or do you want mainly shrubs and lawn?
If it were me, I'd want somewhere to sit out and would use the area where you clothes dryer is and make it into a 'proper' garden to sit out in, but it needs enclosing with hedging, and maybe have a small circular lawn with flower borders all round.
I think you need to imagine the plot as totally separate areas that each have a function- sitting out, play area, fruit and veg, somewhere to dry your washing......
Plan it out on paper and then think about the plants.