Have a look at
www.bristol.gs for some Student-to-Student chat, which should give you some ideas.
If you have a very good memory you might find the exams easier than some but the general feeling is that they are hard.
A bit more difficult than the GCSE/A level etc, you will have to study for these.
As for how many hours too put in, that is down to the individual.
I’m only just starting to study these exams; I think they are difficult but not impossible.
The ground school you opt for will give you all the details you need, or you can call into a flying school and chat to an instructor im sure they will be more than happy to help.