I think lots of people struggle with these type of "projects" because they are longer term, kind of like goals, but different from the other goals we deal with in our lives. The way I would handle "Learn to play the Piano" would be to make that a goal or even an area of focus. I might make a project out of certain parts, as you have done, just to make sure I'm making progress toward my goal. Luckily, your piano mastery goal has elements that lend itself to project-tizing (new word.)
For myself, I think I'd put practice time in my calendar just as I would any other appointment with myself. I might make it an event I could do anytime that day or actually pick a time. The important thing, though, is not to get in the habit of breaking appointments like this or you won't trust your calendar as much.
Best of luck with your very worthy goal!
I am the Party