Hello Aspirant, hope you are doing good.

So firstly, i would suggest you to find out all the colleges that you can get into with your JEE Mains rank, so that you have all the options in your hand. You can use our college predictor tool to find out all the colleges that you can get into with your rank:

https://engineering.careers360.com/jee-main-college-predictor?icn=QnA&ici=qna_answer

Now that you have selected a college for you, however be it,  what type of jobs you will get is in your hand. Definitely college plays an important role in placements, but if you are a really good students and have exceptional ideas that can make you stand out, then definitely you will get nice jobs.

Now coming to your last question, to get into ISRO you have to score atleast 65% in your B.Tech course, then are you eligible, and you have to qualify their examination. Only then you can get a seat in ISRO.

Hope this helps you. Good luck!