What are you doing instead of general maths, right now?
It says somewhere in one of the VCAA documents (very specific, I know

) that Further Maths is meant to be taught with minimal assumed knowledge. It's pretty much based around work you should've covered from 7-10, although I suppose Matrices are probably new.
That being said, it's pretty similar to general maths. I wouldn't say it's necessarily harder, but the content is more in-depth. From a study score point of view - you'll nearly be disadvantaged no matter what (sorry?), because a lot of the stronger maths students do it for that juicy ATAR boost. If you're willing to put in the effort however, you'll be perfectly fine. Chances are if you're coming in from something other than foundation maths (but take that with a grain of salt; I've never looked at it) you'll already be able to jump straight into the work with a pretty good understanding.
Of course, that's just my opinion. If you feel like looking into it a bit further (punpunpun?) check out this stuff:
2016-2018 Mathematics Study DesignVCAA's Past ExamsThe vTextbook Videosand the notes from AN might be interestingAnd maybe the further maths question thread?