Correction: You do FP2 or FP3, you can do both but you don't have to.
AS Maths: C1, C2, Applied
AS Further: FP1, Applied, Applied
A2 Maths: C3, C4, Applied
A2 Further: FP2/3, Applied, Applied
Students can either do Further and Maths at the same time, or one after the other, as they are designed as such.
For engineering, obviously getting M1-4 in there is beneficial. Stats may help you a little bit, but ultimately it's down to you to choose the ones that look interesting to you.