Science

First of all, it depends on one's interest. B.Sc provides you with a better understanding of theoretical science as it leads you in its broadness while B.Tech gives you a practical and applied knowledge of that science.
But from the career perspective, yes, B.Sc isn't as promising as B.Tech is (especially in India) except if one pursue it from a reputed institution (say Delhi University, for one).
And as I said, it's mostly about one's interest.

You are advised to appear for NDA exam conducted by UPSC to become a Commissioned Officer in Armed Forces. Your all education expenses including boarding & Lodging will be borne by Government of India. It is an excellent career option.

Not so early. After class 12th, you have to take JEE Mains and after qualifying it, you can do B.Tech in Computer Science. If you are interested in the further education then opt for Master's degree in the same.
Good luck and have a good future.