My take as a med student now, is that chem is a prereq for a lot of interstate unis so if u want to increase your chance as much as possible then it will be essential to take chemistry into your HSC. But if u are only looking at NSW unis, then yea take literally anything you like and you think you can get a very high atar with. Keep in mind tho out of the 4 med schools in NSW only 2 will take atar into account namely UNSW and USYD, whereas WSU and JMP only use ATAR as a threshold (meaning if u get over a certain ATAR it will no longer be considered) so your interview and ucat becomes much more important for WSU and JMP. Nevertheless just aim for 99.95, 99th percentile, and a fantastic interview.