B.Tech

Check out the link below for marine colleges but you can not pursue marine engineering after one year of B.Tech in mechanical engineering
https://www.shiksha.com/engineering/colleges/marine-engineering-colleges-india-2.

Most of the colleges which conduct their own exams and make their merit list based on the results and it doesn't include your class 12th marks.

Check out the links below for JEE Mains rank and college prediction:
https://www.shiksha.com/b-tech/resources/jee-main-rank-predictor
https://www.shiksha.com/b-tech/resources/jee-mains-college-predictor

You will have to pursue aeronautical engineering in either electronics or mechanical stream as these are the only two eligible branches for taking up AFCAT.

Please refer to the link below for details and apply fee filter of 3 Lacs:
https://www.shiksha.com/b-tech/colleges/b-tech-colleges-Uttar-Pradesh

The date is not declared. You can keep a regular check at the website to know if the admission forms are available. The college website is http://www2.tanuvas.ac.in/

Earlier the Guru Gobind Singh Indraprastha University (GGSIPU) used to organize a common entrance examination for B.Tech which is also known as IPU CET. According to the recent notification, admissions in B.Tech courses in the university will be done through JEE Mains. After successfully passing the entrance examination the candidates will probably have to fill an application form admissions to various engineering colleges affiliated to the GGSIPU. GGSIPU provides admissions to 17 different programmes in 17 colleges affiliated to the university.

Indian Maritime University (IMU) conducts IMU-CET (Common Entrance Test) for admissions various programmes offered by IMU campuses.
For more details, please refer to:
https://www.shiksha.com/university/indian-maritime-university-chennai/imucet-exam

Dear,
There are several colleges but I will tell you to choose the best such as LPU, SRM, VIT and Bennett University.

See, if you are doing this course from a private college then I would suggest you opt for CSE but if you are doing it from a government college like IITs, IIITs, NITs and other state government colleges then you can take any of the course as the placements are good for all the branches in these colleges.