Class 11

First, you should clear your exams. Then, you can think about your interest.

It is of no problem if done before registration which is commonly done by mid-term in 11th.
It is easy to switch from science to commerce or humanities, commerce to humanities but not from humanities to commerce or science or commerce to science (It doesn't mean that it's not possible).
But these arguments were valid till last year. Earlier this year, there were some news about the same.

Hi Anmol,
You should take science stream and in another subject, either you can take IT subject because you have scored good marks in computer science. After that, you can pursue engineering in computer science and your basic will be clear and you will have more knowledge.

You are advised to appear for NDA exam after 10+2 board conducted by UPSC to join Defence Services as an Officer. You can also join AFMC, Pune to become a doctor in Defence Services.

Hi,
It is better to take PCM and computer science in class 12th. In undergraduate level, you can go with honors in any of the subjects from the combination as per your choice. You can also think of B.Stat honors from Indian Statistical Institute by cracking entrance exam after completion of class 12th.

Yes, you can easily get admission in BCA after completing class 12th with commerce stream. To pursue MCA after completing BCA, it is always better to pursue class 12th with commerce with mathematics as one of the subject.

You need a CGPA of 4 and higher to apply to ivy leagues. Your overall profile that includes co-curricular, sports, community services, etc. should also be impressive.