I checked out your island and it looks really cool so far. Some little things that you can consider adding to your smaller open areas are a little cafe, a painting area, a picnic/date area, adding bushes maybe in areas like near waterfalls that are harder to decorate, a garden area/area to grow crops, and outdoor market/shopping area, a pool area, or maybe a playground. You have a really cool setup already and maybe just doing some little projects around the island might be cool but I was overall pretty impressed