justaperson_
It really depends on the person and their level of mathematics knowledge before starting. Some people will find it very manageable and just a normal extension of maths methods.
You probably don't necessarily have to enjoy it to do very well but it would help a lot, being "good at maths" would help too. Usually if someone does a subject that they don't really like they are less likely going to be motivated to put in the time and effort and therefore do worse than if they had done a subject that they were actually interested in.
Yes it contains some physics in the form of vectors, kinematics and mechanics.
There is a bit of overlap between methods and spec, but some of the concepts in spec assume that you understand the corresponding topic in methods.
I did spec in year 12 and found it to be a really good and interesting subject which was quite doable.