Hey there!
Great to hear about your enthusiasm in Maths. To answer your question, 1/2 can be best thought as building the necessary foundations to 3/4. It doesn't actually count towards your ATAR. For VCE Maths, the 3/4 covers very similar content, but does increase the breadth and difficulty of what you're learning.
About specialist maths, it is definitely a subject that you should take. In fact, based on your aptitude and enthusiasm, I'd even suggest looking into doing University Extension math in Y12. Which is conceptually more challenging for much less workload. Anyways, it is probably best to take Specialist Maths 1/2 in year 11. Otherwise you'll end up doing two 3/4 subjects in Year 11, which is very stressful. It is also beneficial to learn Specialist Maths after learning Methods as there is some significant overlap.
Hope my answer helps!