As a student nearing the end of training and having completed most of the ground exams under the old system, I do not know much about the new system. However, from what i've heard at my club, the 100hrs ground school has to be 80% in the classroom. I and still using the old Pooleys books for my final exam, but be warned the syllabus has changed a lot and (not wishing to put you off) but the papers are much harder under EASA. I took the EASA Nav and it was the hardest exam I have ever taken (harder than those for my degree).
As to study before starting to fly. personally this system would not have worked for me as I do not have a technical brain. I logged a a fair number of hours before I started ground exams and this really helped. I would not have been able to do it the other way.
Be aware as well that once you pass your first exam, you have 18 months in which t complete the rest and then ( I think) 6 months to take your skills test after that.
Good luck, hope this helps, and enjoy your flying!