In general, LASORS is a UK summary of JAR-FCL. The UK Air Navigation Order is law and therefore overrides JAR-FCL so you will find some differences.
However, that is not to say that LASORS is correct - it is an interpretation of JAR-FCL and the ANO.
(A)12/18 months?
Originally Posted by LASORS
when awarded a pass in all of the above examinations within a
period of 18 months counted from the end of the calendar
month when the applicant first attempted an examination.
Originally Posted by JAR-FCL2
an applicant shall be deemed to have successfully completed the theoretical examinations for the PPL(H) when awarded a pass in all parts within a period of 12 months.
So one clock starts ticking when you very first sit a paper (regardless of whether you pass it) and the other, from when you first pass an exam. Therefore, sit the hardest exams first!!!!
(B)In the UK, you will sit 7 exams (plus for helicopter (I hope) a type paper). Air Law and Ops are merged as are Aircraft Gen & PoF. From what I remember, you do get longer time and more question for the two merged papers but, don't sweat the small stuff. They are straightforward, not pressured, and you'll have bags of time.
(C) I think you're getting confused here with the professional exams. Private pilot exams are taken at an FTO or RTF usually to the mutual convenience of the school and you. You can sit them at a different school to the one you wish to fly with but each school should agree the handover of results.
None of this is a big deal and I think you're reading much more into it than it necessary. Pop along to your local school, chat to an instructor, have a trial lesson and decide whethr a PPL(H) is something which you wish to embark upon, then go for it.
I hope that helps.
Cheers
Whirls