A bit of symmetry and balance will work wonders in a small structured yard like this.
I'd go for:
3 big pots, one by gate, one by door (both next to path), and one at the other end of the fence in front of the bins.
1 trough planter under the window
Big pots should be big - knee high - in whatever style you like, and the biggest trough thar fits - that way you won't spend your life worrying about cold and drought killing everything off.
Make sure they have drainage, put a layer of stones or broken crocks in the nottom and fill with peat-free compost
Coming into winter you need frost-hardy plants now. I'd go for a central evergreen in each one (or 2 in the trough) lots of spring bulbs (crocus and small daffodils) in the compost, and then surrounding them with trailing variegated ivy plus winter-floqering pansies.
Would look simple, pulled-together and stunning, and you can develop your ideas and have fun from there.
Comeback and post a photo when you're done!