Regular maths on it's own after the first year is plenty difficult; but you definitely need maths to do further maths, it's just a given.
if you're college does it (mine did) we had the option to do an AS further maths course as part of an extra course instead of something like extended project. However the modules in this course really just covered the basics of the new modules, FP2 and FP3 are where the really juicy problems are at, but equally they are extremely difficult.
If I were you, i'd just take all 5 --> just go mental, if you can't keep up then drop your worst and you'll still go plenty far for careers