Career

Yes, you can definitely pursue computer science engineering if you had PCM + economics in class 12th. If you wish to pursue a career in computer science engineering, you must apply to one of these colleges for bright future:
IIT's
PEC university of technology, Punjab
Bengal institute of technology, Karnataka
UTM, Shillong

Yes, you can. Are you pursuing B.Com?

If you want to make your career in aeronautics, then you need to take JEE Mains exam and you need to score a minimum of 55 percent marks in your boards as well.
Top colleges for this course are:
1. Indian Institute of Aeronautical Engineering, Dehradun
2. Indian Institute of Space Science and Technology, Thiruvananthapuram
3. UPES, Dehradun
4. PEC University of Technology, Chandigarh
5. Sathyabama University, Chennai

MBA has wider scope and opportunities as MBA graduates can be employed in all types of industries and all management functions. Whereas, PG Diploma in banking and finance graduates can only be employed in BFSI industry. If you want to work in BSFI industry only then PG Diploma in banking and finance is a good option else you may prefer MBA.

You can chose B.Sc. in aviation.

After class 12th, you can pursue aerospace engineering, aeronautical engineering or courses related like B.Sc in physics and then M.Sc in space technology. You can also pursue courses specifically in telecommunication or space technology or satellite communication etc. There are different courses available. You can also pursue B.Tech in mechanical engineering and then M.Tech in space propulsion systems. This course will help you in entering into space. Also B.Tech in electronics and telecommunication and then M.Tech in satellite communication will be helpful.

Background is never a problem. It is a matter of sheer hard work.

It is not a problem, combining all these pursuits. Even after joining service, you can complete your research and submission of the thesis. Such instances are in plenty. Go ahead with whatever you desire.

It would better if he can pursue Ph.D after completing his M.Sc. He can get better career opportunities.
but u may stay connected to https://shiksha.com for more details