Engineering Entrance Exam

Yes, it is possible. Just fill the PESSAT form once again (Last date to register is April 10). Sit for the exam. If you get a better seat go for it.
More details click here : https://admissionblock.com

Well, it is clearly mentioned in the Eligibility Criteria of GATE that only the candidates with following degree can appear for GATE for pursuing M.Tech.
Candidates with qualifications obtained through examinations conducted by professional societies recognized by UPSC/AICTE (e. g. AMIE by IE (I), AMICE (I) by the Institute of Civil Engineers (India)-ICE IAS equivalent to B.E. /B.Tech. Those who have completed section A or equivalent of such professional courses are also eligible.

More details: https://admissionblock.com/
Yes, candidates need to appear for PESSAT which is an All India Online Entrance Exam for admissions into various programmes offered by PES University including MBA. Candidates can secure admissions into programmes such as B.Tech, BBA in Hotel and Event Management, M.Tech, MBA, MCA M.Sc in Engineering by clearing PESSAT 2018.

KCET is only for the Karnataka students and PESSAT is for all other students. Even Karnataka students can sit for PESSAT. The last date for applying for PESSAT was April 10, 2018.
More details: https://admissionblock.com/

You can do engineering in Coimbatore from CIT, PES, Karpagam, Kumaraguru, Hindustan, SNS, etc.

If u want higher education prepare JEE, if u like normal education mean go with hsc.

You can get mechanical, electrical, civil and biotechnology for sure with this rank. You can wait for the second round and try your luck for other higher branches.
More details: https://admissionblock.com/

Go for KIIT University. It is the best private university.

No, till now, it has not been combined. This year also, the JEE was conducted in two phases only that is JEE Mains and JEE advance. The notifications of any changes will be notified on the official site of JEE Mains.

No, you can't do that now. Once the form is submitted and the examination is conducted nothing about the changing can be done, unless it is done during "form correction" procedure. The form correction process comes many days before the examination. JEE advance offers the last chance to correct the basics incorrect details. But still, the category can't be changed.