Sounds mind boggling to me. Please post the cushion when you have finished.
I am on my way out. I wonder if you googled for machine embroidery for cities like San Francisco that are surrounded by sea and mountains. Or maybe hawai themes.
Oh boy, given it's 10 pm in your neck of the woods you have even less than 14 hrs if you want to sleep at all!
What about making a background on your sewing machine, blue background, lighter blue for the sky, hills cut from different green fabrics, fused to the blue and zigzagged. Some white undulating lines of sewing machine stitches (could be zigzag varying form narrow to wide) to make waves. Then add some embroidered seagulls, some trees on the hills, a few boats.
I think that is a great idea. Plan it on paper and applique the landscape adding embroidery to it.
Then check your beach or bird designs for some sea gulls or a pretty shell grouping.