JEE Main

Sorry, but you have to get 60+ individually in PCM.

Depends on which branch you have opted.

MITS is not bad College. And if interested in Computers than go for IT. MITS facilities are also good. I prefer you to go for IT. YOU can use Shiksha college Predictor:
https://www.shiksha.com/b-tech/resources/jee-mains-college-predictor

You should score at least 130-150 to get enrolled to an NIT.

No, you should not take a drop of 2 years to appear for JEE Main for admission in NIT or IIT. For seeking admission in IIT, you have only two chances.

Hello,
I am attaching a link which will help you thoroughly:
https://www.shiksha.com/b-tech/resources/jee-mains-college-predictor?utm_source=cconnect&utm_medium=CR_JEECP&utm_campaign=7589611

Refer the following link:
https://www.google.co.in/url?sa=t&source=web&rct=j&url=https://www.shiksha.com/b-tech/resources/jee-mains-college-predictor&ved=2ahUKEwjUheP604XcAhUBs48KHfvZCY8QFjAAegQIABAB&usg=AOvVaw1N9BzFtyUCP4JU-2UQHQ0H

What is your HSC score?
Generally, for getting admission in any engineering college you require HSC, JEE or CET score.
If your percentile (50% weightage to HSC score and 50% weightage to JEE or CET score) is above 90 then you can get admission in COEP or VJTI.
Also, if you are ready to take any branch and belong to reservations then you will definitely get admission in COEP, if your percentile is above 90.

As you talk of finance, you don't need to worry about that, you can manage to gain scholarship so that you can go for B.Tech because to move to ISRO you need a platform which you can get through your college. You'll get greater exposure also as doing graduation doesn't mean you go for jobs.