I'm not completely optimistic about the idea and I'm wondering if doing 7 subjects would be worth it or would it be better if I drop Japanese as my subject?
Depends on whether you think you can handle it and what you want to do.
Another thing, I'm currently doing year 10 VSL japanese (I'm in year 9 in day school btw) and would I be allowed to accelerate Japanese along with the 2 other subjects that I'm accelerating at day school? (thus completing vce 3 subjects unit 1 and 2 in yr 10)
This is something I did back in 2012. I took U1/2s of Psych, General Maths and Chinese SL in Year 10, with Chinese SL being taken at VSL. This was OK’d by my school, but definitely a bit abnormal. I often struggled with Chinese, being not very strong in the subject to begin with. I ended up quitting Chinese, took Psych U3/4 in Year 11, and took Further U3/4 in Year 12 normally. I did Japanese SL U3/4 in Year 12 normally at my school instead, so I remember the workload being rather heavy and time-consuming.
Depending on your other subjects, you might find the combination to be overwhelming or OK, particularly if your other accelerated subjects are very heavy subjects.
btw, I really enjoy learning Japanese though
I would consider the subjects you’re doing already and decide based on the following two criteria primarily:
1. What subjects are prerequisites for your future studies after high school?
2. What subjects do you like the most?
If you like Japanese and is worth it, then do 7 subjects. If not, don’t.
Back in my day, it wasn’t heavily uncommon for some students go take a 7th subject, especially so they had a “safe subject” in case they wanted to knock out their weakest subject, but this comes at the cost of lack of time and high chance of burn out. Times have changed since I did high school though, so I’m not sure if it’s common any more.