A level options

i take german, maths & history at a-level (will be studying history & german at uni) and i would definitely say don't bother doing politics. it's not a very academic course and you will cover so many political things in your language courses.
physics and further maths are said to be difficult but will probably assist you with the logical side of linguistics a lot that will be well thought of by unis.
i would also recommend doing english language/english lang & lit if your school offers that because it offers a lot of linguistics/etymology related content that would help a lot
(these are just my thoughts)
good luck

You dont need 4 A levels for any degree subject.
Forget Physics unless you have an interest in doing an Engineering/Physics subject as an alternative degree.

yeah, unfortunately my school doesn't offer either english lang or lang/lit and changing schools isnt really an option
I don't think either physics or FM will be particularly problematic for me - i've looked at the courses with my parents and they both seem ok (both my parents have extensive backgrounds in these subjects)
how should I go about choosing between the two?