Hi and Welcome to MSO
That is ok, I am happy to help with your questions; Just so you know, you will be able to use your gpa from overseas, but the differentiator will be whether you can apply as a Commonweath-supported student or an international student. So if you are an Australian citizen or permanent resident (don't quote me on that there is probably more information on this), you can get a CSP which is much cheaper than international fees. But if you are not either of those, then you will have to pay for international student fees.
1./2 To calculate your GPA, the unis will use your whole gpa from your degree, not just the last 2 years; and to find your gpa you need to get the %age mark from your subjects and turn it into a 1,2,3,4,5,6,7 grade, with 7 - >85%, 6 > 75%, 5 >65% etc; this changes between some unis, but generally it is is consistent across all undergraduate dent unis. Just a quick estimate gives you approx. a 7 gpa considering a 3.3 is 87%, which means you are eligable for all unis -
UPDATED Dentistry Schools Selection Criteria Y12s & Non-standards this will show you which ones - your gpa should be good enough for all (apart from the pre-entry ones, which you can go through the graduate pathway)
3. No, you shouldn't complete a masters because it risks dropping your gpa below what you need, so your gpa is enough already
4. Yes you can, they do.
General info: If you are not an Australian Citizen, you won't need to sit UCAT for any of the unis, although there will be similar tests, like the ICAT for some of them or the MCAT for graduate entry schools; but the cutoff is much lower for international students. UQ, Griffith, JCU are unis that I know don't need these. I am not too savy on the international student side of things though.
If you have any more questions, feel free to ask