so the question is what units/subjects do I have to do at Monash which is the equivalent in melb uni ? Could I just do a physiology major and have the prereq subjects?
Most of that info can be found
here for the Doctor of Dental Surgery (DDS) at Melbourne, including the
prereqs they use at Melbourne and
here for units you'd need to do for any major at Monash starting in 2019, which you can look for second year anatomy, biochem and physiology units that make up the unit requirements. For Monash, I think this translates to the DEV2011/22 for anatomy, PHY2011/
32 for physiology and BCH2011/22 for biochem. Yes, a physiology major would work for the prereq units, I think. I'd confirm all of this info I've said thus far though. (Someone who knows about Monash undergrad --> Melb postgrad med/ dentistry prereqs please confirm, as Melbourne's postgrad med and dentistry seem to have basically the same prereq units.)
im pre decent at math so should I just do the easiest math possible?
Generally, I'd advise against doing this. Every unit you take is approx. $1000, so if you don't enjoy it, you're essentially paying $1000 to hate yourself - not exactly a situation you want to be in. Do a math/ stats unit you enjoy instead.
Also what units should I take across my science electives and other electives?
-snip-
or is it better to do lets say arts or business electives..?
All elective space is yours for the taking, so you do you. As long as you cover the prereqs for the DDS and the requirements of the BSci, nobody really minds what electives you take. Only caveat is that it
might help for a job later on in the future or if you feel interested in, say, doing another science major, that's something you can do too. I've heard rumours of some people doing double majors in, say, biochem and physiology to try to improve their chances for postgrad med and dentistry, but it's not exactly a necessity AFAIK and I don't know if this even increases their chances at all, in all honesty.
EDIT: Made in orange above. I got the unit code wrong; it was PHY2032.