B.Sc

Well, for being an IAS officer, there is a simple requirement and that is graduation from any of the recognized university. If you are planning for being an IAS, I'll strictly suggest you to start your preparations now.
Further queries are welcomed.

Well Tushar, according to me, MBA is opted by students of diverse streams. If you have a little bit of interest towards management, you can go for it. Don't look for a stream.
Now a days, even IIT pass out students are opting MBA.
Yes, surely Science or Maths background will help you to crack entrance examination for MBA. Commerce will help you after cracking the entrance.
I hope you'll do well.
Regards.

You can go for M.Sc. in both the streams. I will suggest you to go for it and after completing M.Sc. you can go for the following stream jobs:
• Biochemistry
• Morphology
• Anatomy
• Cytology
• Ecology
• Pathology
• Entomology
• Bionics
• Evolution
• Ornithology
• Herpetology
• Embryology
• Protozoology
Employment areas after completing M.Sc. in zoology are:
• Biomedical research
• Environmental and ecosystem management center
• Environmental consulting firms
• Educational institutions
• Environmental journalism
• Biological laboratory

The best for you will be to do online courses which will complete your third.You can go through online courses sites like coursera, iitbombayx.in, etc.

Yes, it is possible but whenever you will go for a job, you will leisurely asked- How did you manage? Be prepared for the answer. Both the universities should be different if you are planning to do a regular and distance course.

All fields have equal proportions of good and bad and you also know. The problem is in the period of waiting before we get a job. Sometimes, we can begin earning early in certain fields. Ultimately, what I say is you choose the field, according to your aptitude and you put up your effort. You will find yourself succeeding. Remember, you are young and you will succeed.

Hi Raman,
Admission criteria varies. General criteria is that you must complete 10+2 in science and having pursued medical related subjects such as Biology. Being an international student, you must also take IELTS or TOEFL. Generally, a first class is expected. You must check individual universities to know the entry requirements of separate colleges. You can find university and country information on Shiksha website itself under Study Abroad.
I hope it helps.