Kanpur

Yes, you can get hostel easily as per your rank. You will have to pay total of INR 18,000 per year as fees.
Good luck.

IET Lucknow is better then compared to HBUT
If you want to know more comparison in between these colleges then click on the link given below and watch the video till the end:
https://youtu.be/3YAzEP1vgvQ
If you want to know that apart from these which other colleges that you can get on your rank basis then click in the link given below and watch the video till the end:
https://youtu.be/hOlit6Un7l0

First of all, congratulations brother!
Of course yes. You will get aerospace in any one of the IITs you want because your marks are damn good in Advanced.

Click on the link and watch the video till end. After watching the video, follow the steps as described in the video. By doing this, you could find out the list of colleges which offer admission for you on your rank basis. https://youtu.be/hOlit6Un7l0.

In the first round of counselling, it would be difficult for you to get the Textile Technology and Textile Engineering. But in the 3rd round of counselling, you will be able to get that and yes, if you won't get any of the two, then take admission for Textile Chemistry, as at last round of the counselling, you would be able to get these 2 branches with the help of the faculty there.

You can do MBA, M.Com, etc. for your interest in accounts. Do preparation for government jobs by side.
All the best.

College change or university change after the first year is completely dependent on college and university norms, some university allow it and some won't plus you need to have good scores in the first year to apply for the same.
For further details, contact the college authorities.