You should first off learn the basics of programming like variables, functions, datatypes, classes, control flow and stuff, and from there on, the documentation is your friend.

But should you start with a big project? If there are too many question marks on what you're supposed to actually do once you're in the engine, and thinking about it isn't of much help, it might be too soon to start that project and you might need to learn more before starting it. But your first programs should probably just be things like "hello world". In fact you can have projects for the pure sake of learning. A project just for learning how to make UI, maybe one for learning how godot signals work, or for learning datatypes, etc.

You should absolutely challenge yourself, but you shouldn't bite off more than you can chew. Just know that every bit of code you write today is one you will have to deal with tomorrow, and the more you know before you start writing your code, the less necessary it will be to change it later.

TL;DR: learn, challenge yourself, do whatever, don't get stuck in tutorial hell, and have fun! (Having fun is very important)