In terms of subjects, my knowledge for geo and engineering studies are very limited, but I can offer advice on music 2 and chemistry. Personally, I did not choose music 2 for the HSC, because I wasn't as passionate for music 2 as I was for the rest of my other subjects, but I was definitely considering it. In my opinion, music 2 is very content heavy as you study the context of music in different genres (depending on what options your teacher chooses) and analyse pieces based on musicology (eg. concepts of music +
strong foundations of music theory). Additionally, music 2 consists of performance, aural and composition. Like music 2, chem is also very content heavy because of all the maths involved and understanding why things happen. It also consists of a depth study (basically an investigation of the content you are covering at the time) and overlaps with some of the content you cover in physics (eg. thermodynamics) Both chemistry and music 2 scale fairly well and it is definitely possible to do well in any subject, regardless of scaling, if you are willing to put in the hard work
For advice in choosing your subjects, besides from choosing subjects that you are passionate in (like david.wang28 has said), I recommend choosing subjects according to your strengths - for me, I found that I did equally as well in both humanities and stem subjects, so I chose a mixture of both. In addition, If you have a career in mind, you could chose a subject that is relevant to your degree eg. legal studies for law, or perhaps checking out the relevant syllabus/past hsc exams could be helpful in deciding your subjects. Just remember that if you do end up choosing a subject that you don't like, it is super easy to switch to a different subject - the sooner the better. So sorry this is long, but I hope that this helps you decide your subjects for the HSC!