Degree

If you wish to work now, then find below the career options for you:
https://www.shiksha.com/careers/interior-designer-65

I can see that you are not ready for Masters abroad as of now. You must try to work for a couple of years at a good form where you will gain relevant work experience and develop your personality and skills. Then after if you wish, you can go for an MBA.

You can not two formal degree simultaneously from same or different universities as it is allowed by UGC guidelines on subject.

You can opt for MBA as that will give you management skills along with specialisation in HM.
Also go through: https://www.shiksha.com/hospitality-travel/hotel-hospitality-management/articles/your-career-after-doing-hotel-management-blogId-4630

Yes, it is necessary that you have to complete your degree in 4 years.

Opt for the engineering branch that you love the most and are most passionate about and analyze the future work conditions, scope and growth prospects before taking admission.
You can also opt for psychometric test comprising of Aptitude, personality and career interest to clear confusion.

Your question is a little unclear. As far as I understand, you are asking whether B.Sc in Maths, Statistics and CS equivalent to Bachelor of Computer Science. Well, I don't think they are equivalent. Very rare colleges offer Bachelor of Computer Science. Most colleges offer BE or B.Tech in Computer Science which is different than B.Sc in Computer Science.