It doesn't have to be a big project, to start with. You can allow it it to expand later. My own pet project that has gone through many reincarnations was to emulate my first 'home computer' from the late 1970s. That went from merely emulating the output, through to emulating all the internal hardware, then the user-interface progressing from a CLI shell output, to a curses display to a GUI display.
That project of yours: 'Build one to throw away'. You will learn enough while doing your project that at the end, you will consider your early efforts in producing it to be so bad that you will 'throw that one away' and rewrite it from scratch incorporating all of your new-found knowledge. (Most probably, in doing that you will learn even more and induce you to throw that second effort away too. That's normal.)