Dear Seniors I am Hec scholar, for MS leading to PhD (5 years program) in Mechanical Engineering, currently in first term of study in South Korea. I want to attempt the Css exams in my life, no matter I fail or pass it. I am 24 now, the things I want to know from you are;
1. Is it right decision to go for Css along with studies?
2. How do you compare PhD's with CSP's ?
3. After completion of PhD, most probably I will be an assistant professor. What do you think , its my right decision or not, to go and try for Css exams?
4. I am engineering student, So what optional subjects should I opt?
5. Its matter of my future, I will be very thankful if you reply me as soon as possible as I have very less time to decide.

I am also a mechanical engineer, graduated in December 2016.
1. You can prepare CSS besides engineering. But you are currently studying MS and then PHD, which require a lot of research work. So it is up to you how to manage both together.
2. After PHD you will get a good job and comfort. A good air conditioned office and some lectures to attend. But a CSP's life is different. A CSP can do those things, a common man thinks in his mind only. It will provide you authority to do better for masses. Every group has its own routine and work and requires different mental level etc. For example, PAS, PSP and FSP are totally different jobs. Each person will find himself fit in different groups.
3. It depends upon you. If you are not satisfied with your current life, you can avail the chance of CSS.
4. The optional subjects are selected according to your educational background, your taste and age-old scoring trend.
My optional Subjects are:
International Relations
International Law
European History
Geography.
Environmental Science.

Thanks dear brother

Can you please tell how you got this scholarship? what scheme was it and eligibility criteria etc?

It was Hec overseas scholarship UESTP program for engineering graduates.
You must have BE/Bsc Eng for MS leading to PhD and MS for Direct PhD. You will have to qualify the Hec test, namely HAT test. There is some quota system also, may be Province wise or even district wise.