BBA

No it is not mandatory but if you want to join top business school for MBA then you have to qualify CAT test with good score , today there are many private university and college in which you can get direct admission at base on your graduation degree score and academic record . so there is no need to take so much tension today there are too much MBA college and there are always vacant seats

Select a few colleges according to your location and fees preference and apply for it online from their respective websites. Some colleges do not conduct online application procedure; for those you need to visit the college office.

Select a few colleges according to your location and fees preference and apply for it online from their respective websites. Some colleges do not conduct online application procedure; for those you need to visit the college office.

Diploma and Bba are two different streams. Diploma in mechanical and bba in travel seems no relevance, so go after engineering in mechanical stream for better opportunities

Mba in International business from Iift delhi would be best decision or Mba in finance from top 20bschools will boost your career. Also A LLB degree can be another option if you want to be in financial and legal department.

You can refer this link: https://www.shiksha.com/bba/colleges/bba-bms-bbm-bbs-colleges-in-chennai

for UPSC u should go for BA and then MA in subjects like -
1) history
2) pol science
3)geoghraphy
4) philosophy
5) psychology
and then u can crack upsc exam easily

For all information, refer this link: https://www.shiksha.com/mba/exam/tancet-mba

Refer this link: https://www.shiksha.com/bba/course/bachelor-business-studies-b-b-s-jamia-millia-islamia/10925

Don't know about the other one, but Christ University is taken as the best BBA college in India.