BBA

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.

Dear kiran,
Considering the scope and growth in industry my recommendation is of in "International business" or marketing , coz bith these fields got scope and growth, specially international business.
good luck