To add to the answers to your third question: make sure you do know the fundamentals on the PPL stuff. Don't worry too much about law - PPL is UK law, ATPL is ICAO. However get hold of a set of Trevor Thom books or similar and read through. I encounter people who have made it to PPLs with knowing some of the fundamentals, like what TAS is or even that 1 knot=1 nm per hour.
Anyone else out there not yet holding PPL exams, if you are going commercial make sure you get a solid grounding! Go on a PPL groundschool course if possible. Certainly don't learn it all from the Confuser (a terrible book unless used as back up to solid study). You will be a nightmare for your ATPL instructors, as are one or two students with CAA PPLs from slack clubs that let them get away with awful things in the PPL exams!
SC
Gen Nav instructor, BCFT