Civil Servant (IAS/PCS)

Yes, you can crack UPSC without any coaching if you are perfect in your studies and preparation, otherwise coaching is necessary.
For essay writing you have to do a lot of writing practice.
But, who will tell your mistakes in answer writing, who will correct you. How will you know whatever you have written, whatever you have practiced is right or wrong, at this stage you will definitely require coaching.
My suggestion is, go for coaching for essay writing at least.
Coaching institutions show you a path and if you're really thirsty for IAS or IPS you should prepare.

I depends upon your interest and you must see that the books of which subject are easily available in your city.
But if you ask me about which subject to choose, I would prefer sociology or public administration because these are easy subjects and easily understandable. Besides, anthropology is also a good and competition is also less for it.
But again, your choice must completely depend on your interest.

I don't know much about this topic. But, you may find your answer on the below website on which Dr. Vijay Agrwal guide us for UPSC exam.
http://afeias.com/
Good luck.

By clearing the civil services exam conducted by UPSC, you can become an IPS officer.
Age limit for it is 21-31.
Qualification required - Any degree from a recognized institute.
Rank must be below 300 or 250 (this is not the exact rank it changes every year depending upon the vacancy and requirement.
Try hard to get a rank under 100-250 range. You might also become an IAS officer if you get a higher rank.

It all depends on your skills and interest. Of course, CA is a good choice to make a career.

IAS exam has nothing to do with your undergraduate stream. It is only the minimum qualification to appear in the examination. You may choose any optional subjects of your choice to appear in main examination while pre examination is same for all. You should visit the website of UPSC and find out the syllabus for civil service exam.

You can become an IAS officer by appearing for civil services exam which is conducted by UPSC. The age limit is 21-31 years old. You must have any Bachelors degree from a recognised institution.