Does referring only previous year questions of JEE help us to secure a good rank in JEE

Yes, these will be helpful but before doing that you will have to complete your NCERT properly and practicing over previous year and sample papers should be a secondary thing to do. As once you are done with this better to start doing online mocks, topic and full length wise as this will make you familiar with the exam pattern and will also teach you the time management skills during exam.

Hope this helps!!!

No, every year jee mains question sequence changes...

In order to get good rank make sure your basics are clear. You can refer NCERT books to build your base strong. Referring only previous year paper will not fetch you good rank you need to do lot of practice. You should solve MCQs related to important topics and complete mock test series for your practice. You should also recommended good reference book for your preparation.

Good Luck!!