Hii Aditya,

If you are looking for arts group in BHU, then 250 marks are enough whereas, for admission in Science group, 70% marks in entrance exam can be considered as a good score. For hostel, You have to be top ranked, otherwise you will have to wait for hostel. 

You can visit below link for more information regarding hostel and exam. 

Http://bhuonline.in/pdfs18/UET-Bulletin-2018.pdf

Good Luck.!!