CBSE

Yes, you should. Do your best there and then wait for what happens next and don't think about admission stuff now. Study hard for now and do that part when all your exams are done.
All the best.

Ask the relevant authorities before taking any decision. I am sure you can apply for the same.
Best regards.

If you had given Mains, then surely you are interested in engineering and in those marks, you can also get some good colleges or you can look up for advance.
Regards.

Yes, you are eligible for hotel management. It is based on JEE or your class 12th marks. If you get a merit JEE rank, then you can get into government colleges, or just use your class 12th marks to get into a private college.

Computer Science is the best for the Ethical Hacker.

Yes, you can get, but for the good college, you have to wait till the spot round or the last round of counselling.

You need to fill up the admissions forms of different universities, and then follow the admission procedure.

Basically, the placement will depend on yourself. The more you have taken and have the skills. More you work hard and have the talent, the chance will increase. All colleges are basically same in terms of placements. Try for IITs or government colleges. Maintain your academics as well participate in extra activities too like sports, colleges events, seminar, conference, workshop, etc. It will help you to gain knowledge and experience. Best of luck.