Hi,
I’m not sure if I’m the right person to reply (I personally didn’t do spesh), but since you are very passionate in maths, spesh does sound like a good option for you.
You mentioned that you hope to enter the medical field, so in terms of ‘usefulness’, physics is a good option to take. Physics underpins a lot of the science in medicine, so learning it helps to give you a more ‘wholistic’ view. I’m sure you’re probably also considering Monash biomedical science/Melb biomedicine as your backup courses, and these courses actually have a compulsory physics subject for you to take. So doing physics really helps you there since you would already have the foundational knowledge.
I’m not sure if your school allows this, but have you asked them whether you could take Chinese 3/4 externally? That way you can have 6 subjects that you could take internally, and you could include both physics and spesh. I know that’s a lot of pressure, but if you happen to not like one of those subjects, you could drop one of them before year 12.