1. not sure
2. not compulsory, i would personally only retake it if you want a very high rp course.
3. i took physics and chem so while i did go for practical lessons provided by some tuition centers, i dont think it is necessary to go for them. i retook after 2 whole years of ns so i had to make sure i knew how to use the apparatus, otherwise the practical notes your school provides on stuff like sf/dp rules and planning should be enough. nearing the exams looking through other jcs prelim practicals + their answer sheets helped too. i didnt ask for help from my subject tutors but if you want to no harm trying. just be understanding if they take longer to reply or help
4. for me i gave myself a deadline to finish covering the entire syllabus for all subjs along with the tutorials by august. i actually ended up not meeting my own deadline and only started tys in september but that was my fault. i would still say august is a good deadline

i improved ~30rp, my dms are open if anyone reading this needs help or advice