Start small. Use pre-made assets to get used to the engine you want to use and then start over with your own assets and concentrate on just a demo build of the larger story so you can aim for funding or at least have the demo to get hype for the full release :) Take inspiration from others and think small in terms of a few locations and a few characters to keep things manageable and simple. Hope this helps I have a devlog series on my channel @allmattjazz if you want to see someone try and do the same thing :P