Not so sure of the answer for your first question

Expected average based pay for a non-scholar MX farmer (with NS)
1) Fresh grad: ~3.6K-4.2K
2) with 5 YOE: ~5.4K-6K
3)with 10 YOE: ~7K-8K

Your salary increase will plateau after 4 years+
That Civil Service scheme:
Front load you higher salary for fresh grad at the start to lure you to join.
Thereafter, once you are golden handcuff for the initial years, your skills acquired from public service may not be relevant/transferable for you to go private to command a higher salary. There is no incentive for them to raise your remuneration.

Anyway, farm till retire...it is offered one of the best job security