It's best to start with something small, then develop it. I am inspired by sci-fi and horror series like Supernatural. There are many solutions I can see in other games, and many can be learned.
I would like to play MMO like Supernatural, similar to PoE. Very important in this game was the currency, players could trade between themselves something that resembles exalted orbs in PoE. I would give up an isometric roll and do the same as in games like Uncharted. It would be very important to buy and sell. In my opinion an optimal example is the trading system with the path of exile, where the orbs after the value as a currency have a usable value. For example, you can buy an exalted orb and use it on your weapon, then its statistics will change. In your game too, it would be useful. What is interesting, you can earn it, because to buy exalted orbs need money, a considerable part goes to the creators. If you want to see an interesting buy orbs system then check here, I'm here to buy your exalted orbs https://odealo.com/games/path-of-exile