last bit first - medication is subject to the liquids, gels and pastes rules, so the stuff in tubes can go in hand luggage if it is in the plastic bag. No limit in hold luggage BUT anything that would be a nuisance to lose should stay with you. Of course they have chemists in Australia but who wants to be looking for one if you aren't feeling well?
your prescription stuff MUST be in hand luggage and should be fine. But do check the rules for anywhere that you have a stopover.
save space by taking just a small amount of sun cream and buy it there.