I am hoping to study Economics or Law at Uni (preferably Cam if I get in)
If you want to study Economics Further Maths is a very good choice, as universities are usually more "impressed" with students who study it. Good choice for Economics and as for Law, well they accept anything (appart from General Studies).
I just hope the timetable will allow me to do that comination! If not, I protest...
Have you checked with your school/college whether they are able to offer that certain combination. And don't worry about taking 5 a levels. I take 5 and it feels normal.
No what happens I that we hand in our options form with our choices and a reserve subject, and if there is a clash they tell us and sort it out from there
It is true that studying Economics gives foundation knowledge about it. But a survey has been conducted by UCL and it concluded that students who study it as an A level do worse in their first year don't do as well as those who did not.