Hey there!
I did Physics this year, and from what I recall, there is very little overlap between 3/4 and 1/2.
Algebra is pretty big, particularly for projectile motion, and a good grasp of the trigonometric ratios would be beneficial as well, going into the subject.
So,
here is the study design for Physics. I think the main issues with not taking 1/2 is that you miss out on the electricity module in Unit 1 AOS 2, and the basic force concepts in Unit 2 AOS 1. This second one is the one you'll have to google a little bit on, but YouTube should be able to help if you run into any real issues down the track...
Overall, I'd highly recommend that you take Physics 3/4, as it's much easier to pick up than Methods, and you get to take an A3 summary sheet into the exam, which should fit all the formulae you will ever need...