BCA

You don't need to write any entrance exam for BCA in St. Joseph. Admission is done on the basis of marks obtained in 10+2.
For more details check the link below:
https://www.shiksha.com/it-software/course/bachelor-of-computer-applications-st-joseph-s-college-bangalore-lalbagh-rd-163783

B.Tech is better than BCA. In B.Tech computer science and engineering, you will get more knowledge about various aspects of the programming language and computer architecture.

Yes, you can apply. You have to provide proof of passing qualifying exam at the time of admission.

As you have mentioned, you are looking for colleges offering BCA, this link is been suggested by Shiksha. Com, it has details regarding fee structure, admission process, rankings and reviews. These details will help you to choose the best college in your locality.

Cyber Security is itself an important aspect. However, it also depends on your own capability of understanding the entire subject. You can also pursue CISSP, certification which covers all the aspects of cyber security. I hope this would suffice.

For BCA, you must have any one of subject must be mathematics. You may be from commerce, arts or Science but must have one subject as mathematics. Otherwise you will not be eligible for BCA.

There are over 68 MCA colleges in Bangalore. Please refer to the link provided below for a detailed list of these colleges, along with their fee structures. You should be able to navigate to a college of your choice using the filters on the web page. https://www.shiksha.com/it-software/colleges/mca-colleges-bangalore.

In Eastern India, IEM Kolkata is best for BCA. In 2018, IEM has generated 223 offer letters for only 100 students. 23 students got 1 job offer, 31 students got 2 job offers, 14 students got 3 job offers, 12 students got 4 job offers, 6 students got 5 job offers, 3 students got 6 job offers.