Engineering

If you accept the seat in the first round, then you cannot choose colleges in the second round and vice versa.

Please mention the college name for better assistance
Check out the KCET college predictor below :
https://www.shiksha.com/b-tech/resources/kcet-college-predictor.

For your Community Rank 490, you can get EEE in CEG, Chennai. You can go to official TNEA website and check out with rank details.

Between NIET and GNIOT, CSE or ECE you need to choose first the trade you want to make to make your career in. In terms of placement, NIET got better of GNIOT in last 2 years. Both have good infrastructure, faculty and remember your hard work and dedication will help you to reach your goal.
All the

Yes you can get into Iims. You should score 98 + percentile at the CAT and also perform well at the PI. Join specialised coaching for CAT try and appear as many as possible mock tests & go ahead.

Yes, to a large extent, the syllabus is common. However, the format could be different. In my view you should focus on your B.Tech and only start preparing for MBA open test in your forth year. A sincere effort of 3 to 4 months is enough for open tests. Joining a institute which trains for MBA open

Hi,
If we talk about the graduation level, I would say Computer Science engineering (B.Tech), it will open your way to the real corporate world. You can also pursue Bachelors in Hotel Management that also has very bright future. It depends on your +2 subjects. I would say you can for Amity Universit

No, as your rank is not so good. You should try few waiver seats of good private colleges or you can go for other government institutions like Purvanchal, Rajkiya colleges, etc.

No, you can't change your preferences. You can float with same choice for the further rounds.