B.Sc Physics

By doing B.Sc in any of the courses of pure science, you can't guarantee yourself a stable future in today's world as the value of the degree is not much. But after your B.Sc., you can do your M.Sc, M.Phil and Ph.D. You can end up being a college lecturer or a research scientist.
If you develop any projects then you can have your own start-up and transform it into a big business. So, you have a mammoth number of options.
Hope this helped.

Yes, Physics, Maths and Chemistry is compulsory if you want to do B.Sc (Hons) in physics. There might be some colleges in which it might not be required but in most of the colleges and universities it is an important criteria for admission. So, you have to do your own research in that case.
Hope this helped.

Please check for your eligibility to pursue B.Sc. Physics from the criteria mentioned below:
B.Sc. Physics Eligibility:
Interested aspirants for the course are required to fulfil the below-mentioned eligibility criteria.
10+2 completed from a recognised educational board
10+2 must be completed in Science Stream
Physics, Chemistry, Mathematics/Biology, English are compulsory
Regards.

In combination, you cannot get any college because you can complete your graduation in a single field from all of these either in physics or chemistry or maths.
All three could not be available in B.Sc combined. But, yes, if you take B.Sc maths, there would be combination of physics and maths both.
Hope it helps you.
Thanks

You can consider following colleges:
1. DAVPGC-D A V Post Graduate College
2. AMSD-Academy of Management Studies Dehradun
3. DAVPGC-Dayanand Anglo Vedic Post Graduation College
4. BCMT-Beehive College of Management and Technology
5. SGRRPGC-Shri Guru Ram Rai PG College Dehradun

B.Tech ECE after B.Sc Physics will consume a lot of your academic curriculum duration and you will still be called as a graduate and not postgraduate, I think MBA/ PGDM will be better for you unless you are too passionate about pursuing B.Tech ECE. If you go for B.Tech ECE then definitely opt for M.Tech otherwise if you opt for MBA after B.Tech ECE then you should opt for MBA now.

Definitely. There are many opportunities. Look into research internships online. You can join universities or colleges like IIT for summer research internship as a physics honours student.