What sort of grade should i have to get in Methods, A+, A, B+, to at least be able to cope in the subject?
Any grade between A - A+ should be fine. If you get an occasional B+, that should be fine too.
Also, how much harder is it than Specialist Maths?, is the subject basically 1st Year Uni Maths?
UMEP Maths builds on Specialist Maths in the same way that Specialist Maths builds on Methods. The only difference is that there is a lot of completely new content in UMEP Maths (vector spaces, eigenvalues and eigenvectors, solid geometry, etc.), which will take some getting used to. UMEP Maths is basically a semester of First Year Maths. It is generally considered more difficult than certain subjects like Linear Algebra and Calculus 1. Subjects like Accelerated Maths 1, however, are generally considered to be a little harder.
what happens when i go into Uni, and do say Engineering, will i have to repeat the same subject?
When you enter uni, you can seek exemption from a number of First Year maths subjects, such as Linear Algebra and Calculus 1. I believe you can seek exemption from Accelerated Maths 1 as well. The UMEP Maths course is a little different to First Year Maths in the sense that no First Year student can do it. It basically brings together random bits of maths from a number of different subjects. So in short, no you will not have to repeat the same subject, nor will you be able to.