Civil Engineering

Yes of course. But all depends on your perspective towards study & hard work. Placements are not good but as a whole there's very holistic study environment here.

You may look at this link to get few tips on how to start your own business: https://www.entrepreneur.com/article/235903
Central to any new venture is an idea. You must have your own Independent creative idea to start your own business. Do not look for ideas from others. If you have to succeed you have to have your own innovative idea on product or services which can help your prospective customers to solve their business problem or help achieve efficiency / productivity etc.

No, Dear, 10+2 is compulsory to purse BCA.

You may refer to following link for list of top Civil Engineering colleges in state of Gujarat: https://www.shiksha.com/b-tech/ranking/top-civil-engineering-colleges-in-gujarat/53-2-109-0-0

There is no embargo onnot doing side business with your Engineering studies. Starting new business is 24x7 activity. Are you in position to take additional load without impacting your acedmic performance?

Yeah, you can apply but before applying you must to know about the admission procedure and cut-off for civil engineering in this college. You should get admission by JEE score or CET.