It does generally vary quite a lot, although nigh on all unis follow a general baseline that is expected of a Maths degree. Some go into more depth, some go more into mathematical physics. Some also have more flexibility, e.g. a variety of modules. As an example of that, some unis offer modules in Mathematical Biology - other's don't. It's quite common to see CompSci modules, but again some unis may have different modules.
Most of the time you can find out what's offered on uni websites
Again, difficulty is dependent wherever. (Also note that everything is dependent on uni for every subject). But also, difficulty you shouldn't be worried about: e.g. Oxbridge will have harder degrees than, say, Hertfordshire: but to get in, you need much higher grades and so while it will still be hard, it wouldn't be as hard than if you got in with say, 2 As and a B: it's all relative.
Contact hours will be generally dependent on lecturer/etc. But again, some unis have more time with students (e.g. a Maths degree at Cambridge has around 2 lectures a day, Monday-Saturday, and 2 supervisions/tutorials a week) which gives more help in that way.
Generally, it balances out. Hopefully this gives you an overview of that
. I would really recommend checking out websites though/student 'alternative' prospectuses, etc., to get an idea of how it is. Best of luck!