This is like asking “How many donuts do I need to eat before I should try making one of my own?” Eating donuts might give you some insight into the finer details of different varieties of donuts and maybe even some insight into the ingredients, but it almost certainly won’t tell you much about the techniques, tools, or timing to actually make your own donuts. If your goal is to craft your own donut masterpiece, what you need more than eating experience is kitchen experience. Knowing how to cook will enable you to do more than just cook donuts - you’ll be able to cook all sorts of other foods too. 

If you want to attempt to create a game using that engine, you should practice using the engine to make stuff. It doesn’t have to be a full game, you can (and should) start working on small stuff first - create a new rule, reskin a model, animate a new taunt, create a cinematic, make a hat, or do something creative with the editors available. It doesn’t even matter if your first attempts are totally awful - everybody starts terrible at something before becoming good at it. But as you try, fail, and try again, you’ll earn valuable lessons from your mistakes. As you learn to do things, you can expand your ability to create… and, once you have some context for the creation of game content, you can start looking at what it was the developers of other games did and deconstructing the how and the why.

If you’ve played the game for 2000 hours, you might have enough context to figure out the ‘why’. But you’re almost certain to be woefully inadequate in the ‘how’ department until you’ve actually gotten experience there. Eating ten thousand donuts will teach you how the flavors of various ingredients come together and how to notice their subtle differences, but cooking ten thousand donuts will teach you how they are actually created and give you the skills to come up with your own creations and make them a reality.