Diploma

Hi Hariharan,
Top institutes for PG Diploma in tourism and travel management in Mumbai are listed below:
1. Indian Institute of Business Management and Studies, Borivali West, Mumbai
2. Mumbai College of Hotel Management and Catering Technology, Mira Road, Mumbai
3. Garware Institute of Career Education and Development, University of Mumbai.

No, it totally depends on your interest as there are many career opportunities depending on your knowledge in every course. And doing BA after your diploma is good . You have many opportunities after doing BA so there is lot of things to do in your field do you can go for this.
Good luck.

Yes, you can. You have to appear for many state organizing LEET exams such as DTU, LEET Haryana, LEET, etc.

Top Hotel Management Colleges in India are mentioned at the link provided below. This ranking is based on college rankings published by India Today and The Week. Fee structures for these colleges can also be found at this link. Regards. https://www.shiksha.com/hospitality-travel/hotel-hospitality-management/ranking/top-hotel-management-colleges-in-india/98-2-0-0-0.

International School of Design Kandivali (Mumbai) West provides best syllabus with low free structure and have very well experienced faculty members.

There is no criteria for lateral into BCA course! You have to do 3 year Programme! You can do it through Distance or Part time according to your need!
Good luck!