CBSE

You have not mentioned your stream which you opted for in 12th class, so it is difficult to suggest you something but to become an IAS officer, you need to be a graduate or studying in the last semester of graduation course, the stream doesn't matter if you have a degree, you are eligible. Most subjects included in UPSC are of humanities stream so you need to be good in that particular portion and there will be a paper which is concerned to your subject that you have studied in your graduation so you need to put quite a hard work.
All the best.

Hello,
You said 430 marks. This means, 86% and this is really enough. So, don't worry if you are confirmed that you are getting marks nearby and you can get admission easily. But try to score more marks in JEE mains as Sastra University gives more preference to JEE mains marks.

Where do you wish to apply?

That is not an "important exam", it's "improvement exam". You can go for the improvement exam in this case.
All the best.

MBBS, pharmacy, biotechnology, D.Pharma, etc.

Yes, you can pursue honours in geography. As BA in geography needs an educational qualification of 10+2 with minimum 45% aggregate with any subject.

The course followed by both is almost similar. I would suggest CBSE as most of the government exams refer to CBSE textbooks for their questions.

Hello Abhay,
It is very nice to know your dream of pursuing engineering in aeronautical branch from Madras Institute of Technology. But unfortunately, majority of states in India restrict admissions to domiciles of the state and, hence it is almost impossible for students from other states to get admission. So is the case in Tamil Nadu. I am attaching a link that will give you all the required information about admissions in TN. https://www.shiksha.com/university/anna-university/exams/tnea

Hello,
There is no fee waiver for marks obtained in the qualifying exam. If you scored more than 85% marks, then you can get admission easily in this college or in any college for any course you are interested in. And, you can also get fee waiver in private college.

If your exam centers is close enough to travel in between gap of these two, then you could manage both the exams simultaneously. If it is not possible, there may be the reason of same timing or distance. You should go for your board examinations. It is more important for you more than anything.