A dark grey-green would look great with a charcoal shed, though I like the rustic shed as-is, too. Pink climbing roses would be stunning on fence and/or shed.
White dutch clover is inexpensive, germinates well and would be a pollinator-friendly ground cover in the bare areas, with those stepping stones leading from the paved area to the shed. It wouldn't prevent you from inserting plants there at will. It also adds nitrogen to the soil and is more drought-tolerant than turf grass.
Hosta or lavender along the base of the shed sets it off and is about as low-maintenance as you can get.
Ask on Freecycle and similar sites for plants, pots and supplies; many people have excess to share. Focus on perenniels and herbs rather than annuals.
You can paint pots if free ones aren't the colour you like. I'd think about a theme: terra cotta? grey/green with "french country" imprints and lots of lavender? primary colours/brights?
for example, I determined years ago that I'd have no orange, yellow, red or other "hot" tones in my garden. Only pink, purple/lavender/violet, blue and white. Pots and garden decor are mostly sage green, some greige or a lighter "retro" green. It's gradually developing a pulled-together feel. Green and white variagated hosta for some lightness around the flower beds.
What level of sun exposure does the bare area get?