Computers & IT (Non-Engg)

Being a B.Sc graduate, you would have studied LINUX during your graduation. The syllabus of Linux at Mumbai University forms a strong base for RHCSA (Provided you have studied it logically).
There is a huge scope. Linux being open source is used a lot, mostly by organizations and government too. Also, most of the servers are Linux based. There are very few people who opt for RHCSA. Most of the IT graduates look for web development, app development or software testing kind of roles. A few go for hardware and networking or CCNA. And very few for RHCSA. This will also open up a window for you to explore cyber security and ethical hacking. Go for it. All the best.

Yes,
NIOS students can take admission into BCA without any problem. You just need to make sure that you score at least 45% in your +2 from NIOS. If you can meet this criteria then you can take admission into BCA into almost every college. Remember that there are different criteria for different universities. So, your admission depends upon in which university you are seeking admission. If you want to learn programming languages which you will be studying in your BCA course then you can check out this app which is specially designed and developed for BCA students. It has programs and assignments of languages like C, C+ and Java with their outputs. You'll be studying these languages in your 3 years of BCA. https://play.google.com/store/apps/details?id=technark.bca_courprogramming.

People might talk all about passion and hard-work, but some other things that matter are getting real. Other answers have advice on what language to learn or what book to read, but I will give you some real world advice.
There are three most common pathways to enter the game industry: as a programmer, as an artist, or as a tester. I wouldn't really recommend the third route.
1. Get a degree
The first step is to get a four-year degree. If you're interested in programming, get a Computer Science Engineering degree. If you're interested in art, get a degree in Fine Arts. If you are into writing, get a degree in English / Literature. (Some other distant options are starting out as a game writer, for which a degree in mass media / journalism can help. ). Do not go for diplomas / degrees in animation / game design. They are usually expensive and generally not worth the money that you put in.
2. Intern during summers
The best way to learn fast is by joining a small game studio or company that is looking for interns. It can be a great experience. Or do your own game project during the summer. Gather up some teammates brainstorm and start prototyping an idea. Or go solo and build a game during a weekend.
3. Connect with people & attend conferences
The best way you can socialize with people in the gaming community is by being a part of gaming related forums on the internet and attending conferences. Watch out for local game dev meetups in your city. Announcements for such meetups are usually made NASSCOM Gaming Forum. Some conferences that will be of interest are:
NASSCOM Game Developers Conference (Pune, November each year)
Casual Connect Asia (Singapore, May each year).