M.Tech

Check out the link mentioned below:
http://entrance-exam.net/jobs-after-mtech-in-mechanical-engineering/

M.Tech in aeronautical engineering is considered to be the most preferred post graduation degree in the field of aeronautical engineering.

Since you are working, it is one of the options. It may not carry the same weight as a regular M.Tech but would be an added qualification.

Its depend on the college, university & government. Most of the engineering colleges provide merit & merit cum means scholarship. You should discuss about this in the college in which you are interested.

No, IGNOU do not offer M.Tech course, for the details of master courses offered by IGNOU, check link below:
http://www.ignou.ac.in/ignou/studentzone/programmes/2

The placement for mechanical is not that good if we talk about mechanical branch be it NIU or any other college as you don't get to see so many companies coming in for core branches. So unfortunatley the placement record for mechanical is not good but this time we are expecting new companies like Tata to come for placement. Hope answer helps.
All the best.

It depends on your skill set, technical ability, personality, specialization and how you crack the interview.

There are plenty of job opportunities available to M.Tech CSE graduates. Everything depends on what do you have to offer to the companies. There are many many different Job Profiles available for M.Tech graduates. Mobile Apps Development, Web Development, Testing, Product Development, Business managers, Analysts, Data Scientists etc. I would suggest you to specialize in some comparatively newer technologies like Cloud Computing/ Virtualization.
As per my knowledge this specialization is available in Anna university, UPES Dehradun & VIT Vellore.
Hope you find this information helpful. Good luck.