Hello hello! It's great to see you around the forums, and you're asking some very great questions too!
Congratulations on finishing Year 9, and I commend you for thinking about VCE so early.
1. Should I even be worrying about preparing for VCE at this point? I've already started some research on which subjects I should pick, but beyond that I've basically just been trying to focus on school work and developing good study habits.
I think that, as you mentioned, using Year 10 to create good habits is something that will be beneficial to you and is certainly going to be applicable to life during VCE. Even creating good habits outside of your study around sleep, eating, drinking enough water and exercising are good ideas because when you're life gets busier, you'll have something to fall back on. In terms of preparing for VCE, figuring out what you enjoy in Year 10 and researching subjects for next year sounds wise. Outside of that, I wouldn't spend too much time trying to prepare for VCE. If you're doing a 1/2 subject, focusing on learning that content really well and being really successful at that is another way you can help prepare yourself.
2. Is it better to do 3/4 Psychology or 3/4 Biology in year 11? I'm thinking of doing both of these subjects in VCE (they seem interesting), but I don't know which will be better to accelerate and which is better to do in year 12.
I'm currently accelerating biology and very much enjoying it. I think that it's a matter of preference. Biology has been a good subject to accelerate because it doesn't rely on you having heaps of knowledge and skills from other subjects (like physics would) and a lot of the learning is content based (but they are slowly moving away from this). I think that both psych and bio are good options and it comes down to a matter of personal preference. Perhaps someone who has completed both could give you some more advice.
3. What can I do right now to better prep for Year 10/11/12?
The main thing I did in the summer holidays between year nine and ten was focus on preparing for my 1/2 subject and preteaching myself a lot of content. I found that absolutely invaluable and it is what I plan to do for all of my subjects this year. Also, relax. And enjoy yourself.