I would recommend studying pretty hard for those half-yearly exams, rather than cramming for them. This way, you won't need to study this earlier stuff again too carefully before your trials. In the July break, you will have more work than you bargain for, especially if you're a umat candidate.
Undergrad med at unsw/monash is really hard to get into. You need a good atar and a good umat, then perform well at the interview. Tbh if you're aiming for one of them exclusively, save your soul and go for pstgrad. If you're happy to trek out to newcastle/une/uws (which are good unis for med)...
If you have submitted all relevant documentation for the uni courses you have applied for, then no you've done everything you need to do until offers come out. And I don't think it matters if you change or not, because you will get an offer for the highest preference you are eligible for...
If anyone is reading this who is currently doing Latin, post any questions here.. I presume a few people with state ranks will be able to help you out!!