Hi! I am one of those crazy children who will have completed all three levels of vce mathematics by Monday week, so although I don't know your exact position or desires I can understand where you are coming from.
I believe that maths is an incredible discipline, however I do agree with the above that too much is potentially not the greatest. Speaking personally, last year I did 3/4 Further, 1/2 Methods, 1/2 Physics, 1/2 English and U1 of Chemistry. I only completed unit 1 of Chem (dropped it for art and then picked up psych this year instead alongside spesh) because
I couldn't keep up with the demands required for that much science and math. My marks were good, but my stress levels and mental state weren't, and making the decision to add more diversity to my subjects imo helped to keep me sane.
Again, this is one persons experience and of course should be taken with a grain of salt. Echoing what was said by Joseph, only 2 of 3 vce maths may be in the top 4 so that may weigh into the decision making process also.
It is clear that you want to go to university to study something, and based off that alone my recommendation is to maybe consider something other than further, it really isn't a prerequisite for anything.
Take as much or as little away as you would like- at the end of the day this is your education and you know yourself, your interests and your ambitions better than anyone else. Good luck for 2017, whatever choice you make