Is it better for me to do 6 subjects?
It's ultimately up to you, but 10 units means less work/study, while 12 is safer if you screw up a subject.
I'm kind of leaning towards math general as I heard it scales really well if I get over 95% compared to getting a 80 in advanced, what should I do?
General Maths always scales poorly.
In the 2017 HSC, an HSC mark of 95 (top 1%) in General Maths was scaled down to around 85.
But anything below the top 5% will severely impact your scaled mark.
An HSC mark of 81 in 2U Maths (top 50%) was scaled down to around 65.
But in terms of scaling, 2U Maths is far more generous than General Maths for marks that are below the top 5%.
So if you're capable of 2U but choose Standard Maths, then you have to make sure you ace it to end up with a better mark.
https://www.uac.edu.au/assets/documents/scaling-reports/Scaling-Report-2017-NSW-HSC.pdf (p.39)
English Standard vs. Advanced is a similar scenario.
Also, some uni courses will assume or require 2U Maths, so if you choose Standard Maths and then change your mind later (say, you want to do engineering or a science), you may have to catch up.
Finally, if you're capable of extension Maths then you should seriously consider it, even if your uni course may not require it.