What fun! It’s a lovely project starting a new garden. As others have said, improve the soil now, while you’ve a bare patch and monitor the sun movement around the garden.
Also, Autumn is the best time to plant shrubs and plan for where the cottage annual will go in the Spring.
I’d draw a measured plan of the flower bed, just to give you an idea of where things might go. You might think about using the fence for climber or espalier fruit trees.
Now is a good time to go to nurseries and garden centres, as they begin to sell plants off cheaply, they don’t want to overwinter them. Especially if you want some larger specimen plants. How about a pergola to give height?
Now is also a good time to plant spring bulbs, that will give you colour early in the year.
Have a look at Pinterest’s small garden suggestions, it’s often a good place to give visual inspiration.