Its all about how you practice, and how you set your goals. If you aim for winning every single tournament you enter, you will improve MUCH faster than if you aim "i just wanna get out of pools".
/rant about how you should think
Its not a matter of going into every match and thinking "im gonna win", its when every single time you think about the tournament, you aim for the top. You need to practice and prepare like you're gonna win, and if you do that, you're gonna improve way faster than anyone else.
Setting your goals "unrealistically high", does, no doubt, make you less "happy" in the beginning, since its much harder to reach your goals, but if you wanna be the best and improve fast that's simply what you're gonna have to take.
As for the question: I could do everything fundamental with falco after 2 weeks of playing the game. You need to focus on implementing about 30% of your characters options, the most important ones, and getting them to a level where you can do them without ever having to worry about failing, and then as you go along you can start implementing more.
After about two or three months I really needed, and after that I could really start working on what really matters, reading your opponent, learning matchups, and so forth.
Please don't focus on random technical stuff, its not what really matters. That will come in time anyway.
