As with any game development tool, the key to success with Unity is iterative development. You have to build in manageable increments - be ambitious, by all means, but be ambitious in small chunks, and arrange those chunks such that, even if you fall short of your ultimate ambition, you’ll at least wind up with a coherent product. Get the most crucial elements in first: have an idea in mind of your ‘minimum viable product,’ the simplest, most bare-bones thing you could possibly create and still feel as though you achieved something worthwhile. Get to that minimum viable project before moving on to larger ambitions.
This tutorial gives you a strong starting place, but the best way to learn Unity is while building a game. Start building a game, fill gaps in your knowledge as they come up, and the gradual flow of knowledge will erode away the things you don’t know surprisingly quickly. Unity is a powerful tool, and with a bit of exploration, you can be building impressive projects with it quicker than you might expect. Good luck, and enjoy Unity!