The whole window will have a one foot wide window sill. I will have to show you the place to get a good idea of things. Basil planted in teacups for the kitchen, cheap and pretty teacups planted with fresh herbs on the window sill.
Keep egg shells in open container in fridge. When the container is full, crush shells into small bits and sprinkle them around base of your plants. Sharp eggshells will deter slugs, snails other bugs & adds touch of calcium to soil.