Government & Defence Entrance Exam

Yes, it's degree is valid, as it is a national University.

After completion of your class 12th, you can join Indian army as a soldier. Just fill your form online or join Indian army, as per your district rally and go to the rally and participate in the physical test of Indian army.

Hello,
The Railways Exam is conducted for different posts in Railways. Including the technical and Non Technical Posts. One of the post in Railways is RRB ALP or Assistant Loco Pilot Exam. Recently the government. And RRB Board has recruited the various candidates for the Railways Assistant Loco Pilot Exam. The RRB ALP Exam would be conducted in different phases of Computer Based Test. You can prepare for the RRB ALP Exam check out the Syllabus-https://scoop.eduncle.com/rrb-syllabus-exam-pattern of RRB as the Exam is conducted in the given subjects -
Mathematics
Technical Ability
General Awareness
Arithmetic
Reasoning Ability.

PG Degree is the best and rational choice for you. I don't mean to discourage you but see that you are at 30 and a degree of PG will strengthen your career efforts. Whole doing PG, you can keep your preparation for UPSC on. But I shall not put your UPSC aspirations first over Higher Studies.

Below link may help you:
https://www.quora.com/What-are-the-salaries-of-IAS-IPS-and-IFS-officers.

Arihant publications books, 10 standard Ncert book and previous year papers is good for preparation of the BHU CHS 11.

No, officially you can't, because eligibility criteria for NDA exam is that you should have passed class 12th class before the SSB interview, as you have to present class 12th marksheet during the time of SSB interview. But yes, if you meet the age requirement, you can apply for the written exam, and then you would not be able to appear for the SSB interview. Also, as the exam will include the syllabus of class 11th and class 12th, so there is no benefit of appearing in it now. So, you should appear after class 11th that too for the written only not SSB.

Any Bachelors programme is eligibility for civil service exam. The minimum age is 21 years. IAS is a tough programme. So, if you are interested in civil services you should prepare for the UPSC exams.

Depending on kind of jobs/ career do you opt for. If your interest lies in career directly in management side then MBA is better option but you wish to be in technical side and then grow in administration then M.Tech is better. Whatsoever you do, do from a reputed institution like IITs or Iims. UG can be done from any private also but PG only from these institutes as branding/ stamping and depth of knowledge matters more otherwise you'll suffer through a career. All the best!