USA

You must take SAT or ACT and TOEFL to pursue Bachelors degree in USA. If you are interested in engineering you must be very strong in mathematics and must have a good SAT score. In addition, you must have good extracurricular background and a strong profile.

Yes, you can. But, it would be better if you complete your Bachelor from India itself and then try for Masters abroad as it will consume a lot of time in gathering documents and qualifying various exams to settle abroad.

Go for USA, that's better.

You don't need to worry about 3 GPA. It is for EEU or American students. For Indians, we have to qualify IELTS and GRE exam as per the demand of the college.

You can get admission in the University of Florida. It will cost you around 12 lakh rupees.

Yes, you can pursue MS in civil engineering. It has a good scope. You should opt for MS in structural engineering or construction engineering and management.

You should opt for aerophysics course.

Please visit the links mentioned below to find the tuition fee, you must explore more and also write to these universities for any updates.
Indiana University
https://studentcentral.indiana.edu/pay-for-college/cost-of-iu/index.html
Rice University
https://graduate.rice.edu/costofstudy
UNC
http://finaid.uncc.edu/aid-basics/estimating-costs/graduate-cost-attendance

294 as a GRE score is very low for top ones. Utah State University, University of Denver or University of Delaware may accept you but check the application requirements. You should opt for universities below rank 40.

HI
I would like to address this under two separate issues/process
Admission - There are few schools in the US which are not ranked, but may accept students without SAT.
Visa - There are hundreds of students applying for the student visa for higher education in the US. Most of them have taken the SAT, and then there are few students applying for a student visa without the SAT score. There is going to be a comparison. Visa officer may think that a student without the SAT score is not a serious student.
Hence, it is advised to take the SAT for not only getting into a ranked university but also for a better visa result.