MA: Again, will need to do well in the externals but your rank is incredible, very impressive SO if your cohort does well in the externals (including you) you will do extremely well (possible/likely band 6)
P: I did the same test and got 75% and am also coming first, so we are pretty much even, however, we will both want to concentrate on this also as it scales very well, however, since you are first, you control your fate
Note: School rank does not matter in the final result, that would be to bias, however it is your cohort, and since you are ranking well in all your subjects, you are in a nice position
What should your priorities be? (in order from most to least): Chem, Maths Advanced, Mathematics Extension (get it to about 70% and you will be fine), Physics, English Advanced (I place this this low because all I am doing is remembering essays, EASY!!! you should too), SOR