Engineering Scope

1st option:
It is good for you to join MBA through distance because, with distance education, you will be able to do a job as well as MBA. (Prefer this only if you are economically weak).
2nd option:
Start preparing for CAT exam, do your best in CAT and get admitted in the top MBA college in India based on the CAT score.
(Prefer this if your economical background is strong).
Course Expenditure
For the 1st option:
An average of approximately 1 lakh (low possibility for getting education loan).
For the 2nd option:
An average of approximately 2-5 Lacs (maybe less if not in top MBA college) (high possibility of getting education loan).

The upper age limit for junior research fellowship ( JRF) offered through the National Eligibility Test NET 2018 is increased by two years, making it 30 years. There is no upper age limit for applying for eligibility for Assistant Professor. For details refer to the link: https://cbsenet.nic.in/cbsenet/eligibility.htm.

Yes, a lot of people have done that. You need to do a three year LLB course (instead of the 5-year course of BA+LLB. The minimum requirement of law is to have done graduation before you can do LLB. Most people prefer BA+LLB. So, as to get the law degree in minimum time (5 years).
People have done law after engineering, MBBS, B.Com and almost all Bachelors. Delhi University (Faculty of Law), Government Law college Mumbai and a lot of colleges offer 3 year law courses. For more information, google 3 year Law India.

After announcement of JEE Mains and advanced result, there will come a schedule of dates of round of counselling and instructions by JOSSA. You Fill colleges in depending priority. Now you should focus on entrance examinations.
Best of luck.

Some of the top tips and tricks which you can follow for IIT-JEE preparation is mentioned at the link provided below. To get a good rank in JEE and make to the IIT you need to have a strategic planning that suits the present format of selection. The present format demands an all-around performance as it considers your board examination, JEE Mains and Advanced. Mentioned in the link provided below are such tips and tricks to help you with successful preparation:
https://www.shiksha.com/b-tech/articles/10-tips-towards-your-jee-mains-advanced-preparation-blogId-11721.

Yes,
You can pursue CA after engineering. At first, you have to know that CA is considered to be the most difficult stream in commerce. It usually takes 5 years to complete the degree. However, students fail to pass it at one go. Hence the number of students passing CA is pretty low. Also, students who do not have a commerce base its much tougher for them. Finance and accounting is something which you need to learn first. You need to put in extreme amount of labor.