C1 - peasy, should be aiming for full UMS C2 - peasy, should be aiming for full UMS S1 - slightly tedious, but not too difficult if you can be bothered to learn the content S2 - slightly tedious, but not too difficult if you can be bothered to learn the content M1 - dull and quite tricky! (If you're lucky, your school may let you choose just stats and perhaps FP3).
It does 'merge' somewhat, but FP1/FP2 will allow you to discover a whole new world of maths! (Matrices, complex/imaginary numbers, properties of polynomial roots, polar coordinates, more hyperbolic functions and properties of curves and inequalities), so should be very interesting for you if you enjoy the pure side of maths.
i think that core 1 and 2 wont be too bad, as in algebra 3 now i cover most of core 1 and 2 is just extended gcse level. my school attempted to teach us stats in year 10 and i found it awful, which is a concern
i done maths, chemistry, biology a year early and got an A*, but i assume a levels as vastly harder than these
well obviously they are, haha. if you come out with majority a*s and a few a's then you're the kind of person who would survive doing the subjects you've listed.