Some universities do not like candidates to study both business and economics due to their close nature, acting as ‘revision’ for one another. Check universities you fancy for their entry requirements for subjects to make sure this isn’t the case for your chosen choices.
You do not usually need FM, but it can certainly be useful. Most universities also do not require 4 A Levels so it may be better to do 3 and focus on those, doing whichever of the two subjects would best benefit your pathway.