India

Best Colleges for BTech Mechanical Engineering are as follows: IIT Bombay, College of Engineering Pune, VJTI, VNIT, SPCE, VIT Pune, AIT, DJSCE etc

MBA in Australia is a good choice unless you are ok with their fee structure. You can also try US universities as well. They are far better compared to Australia

MCA graduates from reputed Institute are in good demand in Indian IT industry. Starting salaries are in the range of Rs 3 Lakhs or more per annum.

Top colleges you check on https://shiksha.com according to your priorities.
Some colleges already started giving out forms. Some colleges are waiting for CBSE results to get declared.

No sir entrance based

Hey Mohemmed M,
You don't have enough marks in JEE Mains to get NIT or IIT but you can consider following options.
You have few colleges performing really good in south India. You can consider taking admission in these colleges as they are good at placement records as well as rankings from industry. M

Hey Darshil,
There are chances that you may get NIT based on your score in JEE mains based on your caste. But you should not rely only on a single option. You should also apply for some other best institutes either government or private. You can also expect scholarships from some private universities