I fully endorse a fantasy setting for your game. It gives you so many more options for story telling. When a character in what seems like a normal suburban setting finds a magical ring with special powers it takes more effort to suspend your disbelief. When a character in a fantasy world finds a magical ring it just fits the setting. You can have strange creatures and impossible situations, go nuts. Past that, it's okay to indulge some fetishes. A little bestiality or futa or whatever you are into. Trust me, other people are into it too. That isn't to say everyone will be down with it. So if you are worried about it putting certain people off, you can try making it optional. Don't feel like you HAVE to though. Just let people know up front that it's in the game.
So, assuming you do want to use a fantasy setting, here's some advice I have on doing it. Establish the rules early. By this I mean if you have some weird doodad that does something, make it clear how it works. I mean it's great to be mysterious about certain things, but what you want to avoid is the feeling that things just do whatever you, as the story teller, needed them to do. I mean this is story telling 101, but something like the sword Sting from LotR. You get told right away it glows when orcs are nearby, so later when it glows the reader/viewer goes "oh shit, orcs." Now imagine if it hadn't been explained. The sword glows "Why is it glowing?" "Oh that means orcs are nearby." It feels like it was just pulled out of nowhere. It's a fantasy world, you can't rely on pre-established rules. "Everybody knows that kind of sword glows near orcs, duh." Even if you want to keep it vague for story reasons. Like oh this magic medallion will "keep you safe" then at a crucial moment when the hero is about to die, the medallion activates and teleports him to safety then crumbles to dust. If it's going to be vague, it should do like one thing. If the hero is going to fall and the medallion makes him fly then later it stops an arrow then later it detects poison in his drink it's like okay what the fuck doesn't this thing do? I'm hoping you already knew this, but I figured I'd throw it out there.
Good luck on your future project.