Diet and Hay
Diet and Hay comes up sooner than most beginners expect. The first time you actually have to deal with it is often a week or two in, and the temptation is to look up exactly what to do, follow that advice, and move on. The trouble is that diet and hay responds to the specifics of your situation more than most other parts of rabbit care, and generic advice tends to almost work and then slowly stop working.
A more durable approach: understand what diet and hay is for, not just what to do about it. Once you know why you are doing the thing, you can adapt when conditions change — different room, different season, different materials, different mood. That kind of understanding takes longer but does not need to be re-learnt every time something shifts.
A final note. The aim of rabbit care is not to look like someone who does rabbit care. 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 health checks. Most of what is good about the hobby will arrive on its own.