Ok, so here's my advice, according to your constant change of themes
Maybe you should just try doing your own thing, or a mixture of different themes. When people visit my island they think fairy/cottage core. Which is only half of my actual idea. My decorating is going to vastly change, so I think maybe dont have a completly solid theme and do as you please
My old island before this one was all over the place, didnt have a solid theme, but I made it look nice kinda,
City, fantasy, horror, core was what my visitors saw on it. But I was honestly just doing what I wanted, I even had refrences to favorite series/fandoms, it's kinda fun to not go in with a plan and do as you please
This current one is pretty much the same, I have paths, and things I made for it and it fits a few themes. Mainly cottage and fairy, from the designs. Also an idea But it's still gonna be personalized
My side is gonna be suuper playful, and floral. Just because pretty much all my villagers have the play hobby. Only three arnt spazes
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So maybe you should just do your own thing for awhile, then maybe inspiration hits you. I was looking for something to do with my museum, and decided on a dinosaur zoo.
Themes can also change, my old island was susposed to be completely based on my novel, but turned into something else, my villagers were even planned out before hand, but aside from Marshal, changed by alot. But I still cant imagine parting with them. But hey, creating my own thing with no limits also gave me lots of great memories.
Pitfall, magical girl dress, sanrio clothes, the list goes on. Though I'm a bit picky on clothes now, I'll definitely be dragging them through random stuff too. But Raymond was held by my friend, so hes the only poor soul to remember everything lol.
But yeah. In the end it is your choice, but maybe just trying out your own thing, keeping in mind that you have no limits, because that's pretty much how alot of island tours start, not all of them, but most do, then morph into something else.
or maybe you'll come up with a theme for it.
But honestly dont hold yourself back, this game is about creativity, so dont second guess, and come up with your own theme