Dear aspirant!

Jee mains previous year question are most important part of one's preparation. Solving previous year question will help you figure out the difficulty level of asked questions and you will observed that many of questions are repeating in next year.

Yes, you should solve jee mains pyq only after practicing the back excercise of ncert books as then you will follow the proper format that is easy to hard. You can also set a target of completing minimum two chapters a day as exams are most expected to occur in February 2022. For chemistry, i would especially suggest you to read NCERT minimum three times to score good marks in this subject.

All the best.