I think it's hard to go wrong to just pick a course and step through the whole thing, including the stuff you feel like you already know. I say "feel like" because I've seen many posts here from people who did that and were surprised to learn new things even though they felt like they already knew the course material. I had the same experience.

GT does a good job of structuring courses in such a way that one thing builds nicely on the next. It seems to me that the scattershot way of doing it removes most of the benefits of GT's curriculum and takes you back to the "watch random YouTube videos" method that tends not to be a very good way to learn.

Stepping through a course that includes things that you want to learn, but doing so in order, allows for a better learning experience when you do get to the skills you want to learn, allows you to begin to form a teacher/student relationship with the instructor, which enhances learning, and takes full advantage of the work that GT has put into how to teach skills. And our brains tend to learn better within an organized, cohesive curriculum, which is why the "random YouTube video" method doesn't work -- dare I say ever?

Of course you will probably go more quickly through the lessons that you're already strong on, but that's still a good solidfying of your skill set.

Hope that helps!