Hello, good sir. Thank you so much for your models! Devilsaurs, fel reaver, core hounds exist in the Warcraft lore. Now they will appear in the maps for Warcraft 3.
When working with your models, you mostly inspired by updated WoW models, or their older counterparts?
Scribble down your ideas, worlds, characters and story on paper, books and notepads. That's how I started.
Check out videos on Game Design and world-building, there are plenty of great videos, tutorials, lectures and advice to be found on youtube.
One common mistake people do is creating a massive world with unstoppable characters. Start small and let things evolve with time instead. Give each component in a world certain meaning and importance.
Getting carried away is good as you might come up with unique ideas you can scribble down and use for later but you'll quickly find that most good games work around a small set of rules and core design. Chess for example is extremely simple yet most people can grasp it quite fast and enjoy it. Even come up with strategies and their own style of playing.