First of all, Welcome to CSS Forum!

Good to hear that you want to appear in CSS 2014.

1. Is it actually useful to go to an academy to get the basics of the exams? Do they teach students things which we can not learn from books or the internet?

Not the institutes, but your own will power can bring you to the understanding of particular subject.
Thoroughly go through the CSS forum for each subject, you will find the very useful Threads/posts regarding subject guideline.
Then subject selection, or subject basics will not be any more problematic for you.

2. Time. I have heard people saying that ''you will have to study for 10 months daily and for 8-10 hours, stop any social activities and stay at home all day and study!'' - How true is this? Frankly speaking, i have never been able to concentrate more than just a couple of hours at a stretch. Will i have to change my self for this ?

As its totally depends upon you skill. If you have good writing, reading skills, you will surely cover in less time. Its better to give 6-8 hours will full concentration than giving 10-12 hours with here and there concentration.

3. Subject selection. First of all, what do experienced people suggest - is it better to have more subjects because they might be easier for you or is it better to study less subjects because there would be lesser subjects to study? For example: I have come up with a couple of combinations but have not decided yet because i want to study the syllabi further.
Option A: Public Administration, Sociology, Journalism, US History, Constitutional Law and International Law.

Option B: Economics, Sociology, Journalism, US History and International Law.

Option C: Economics, Political Science and Islamic History.

Go for the subjects in which you have the basic knowledge. History subjects like Islamic history, are easy tocover because no need for the guidance/tutions. You have done BBA, you can go for your field subjects. Language subject selection is also useful.
Further, don't make your elf confused, go for the subjects which you can easily cover.


5. I am currently working full-time and plan to leave my job around August/September so that i can fully concentrate on CSS preparations because these days i only have some time on the weekends. Would you recommend this? Or would you suggest that either i keep on with the job, or leave it next month i.e May ?

If you think you have to give proper time otherwise you can't cover the subjects, then you can plan for leave. If job really doesn't dist rub the preparation then dont go for the leave.

Now decision is Yours.

Best of Luck!

__________________
Beauty