JEE Advanced

It isn't based on the percentile. It is based on the marks. By converting percentile into marks you will be able to know your total score and compare it to the given cut off. As expected cut-off is 100-110 for JEE Mains 2019 paper 1.

Please visit this site first
https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.shiksha.com/b-tech/amp/jee-advanced-exam-cutoff&ved=2ahUKEwiE8_ii-7vhAhUPb30KHS0BA4sQFjAAegQIAxAB&usg=AOvVaw2GsiHozkaSgJ6Wm_XzSMNI&cf=1.

Please visit on those site-
https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.shiksha.com/b-tech/amp/jee-advanced-exam-cutoff&ved=2ahUKEwiE8_ii-7vhAhUPb30KHS0BA4sQFjAAegQIAxAB&usg=AOvVaw2GsiHozkaSgJ6Wm_XzSMNI&cf=1.

Please visit on this site-
https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.shiksha.com/b-tech/amp/jee-main-exam-cutoff&ved=2ahUKEwj2keTL-rvhAhVRWisKHV8hBrkQFjAAegQIBBAB&usg=AOvVaw0iFAYbXCMPRZzeFBDWnX1Z&cf=1.

As there will be two JEE Mains exams this year, so after first exam only the percentile has been released right now. However, after the second exam that took place, everyone will know their ranks on the official website only. Thereafter, the marks needed to qualify will be disclosed after the second exam result that took place in this April.

Yes, you will qualify for JEE-Advance. Your expected rank is about 166666 and around 2.2 lacs candidates will qualify for JEE-Advance. Therefore, your chances are very high.

No problem, attempt the exam now.

If you are confident enough that you can study for one year without any diversion. Then yes you can. I am a dropper and I was self motivated to crack JEE with a very good score. And yes I did it. Everyone is capable of doing it, just don't lose hope and work hard for a year. The amount of effort should be much more than you put in 12th.
All the best.

You should improve your score in order to get eligible for JEE advance if you are a general category student.

JEE Advanced is specifically conducted by the IITs to admit students.