First Headphones
There is a temptation to treat first headphones as a checkbox to clear before moving on to the more interesting parts of headphone audio. That is exactly backwards. First Headphones is where a real understanding of the craft starts to develop, because the small choices you make about first headphones reflect almost everything you have learned so far. People who skip first headphones hit a ceiling within a year and cannot see why.
The other way round: time spent on first headphones pays compound interest. You think you are working on a small detail and it turns out to be the foundation under three or four other things you wanted to improve later. If you are choosing what to focus on next, choose first headphones more often than you think you should.
A final note. The aim of headphone audio is not to look like someone who does headphone audio. It is to enjoy the doing — the slow build of competence, the small surprises, the days when something just works. Keep the gear modest, keep the schedule sustainable, and pay attention to comfort and fit. Most of what is good about the hobby will arrive on its own.