McMaster University

You can pick an OS between Windows or Ubuntu. As majority of Indian colleges operate on Windows, there are few colleges which operates on Ubuntu. I haven't seen any college operating on Mac. So, it is better to stick with the technology used in your college. If you want to learn programming languages which you will be studying in your BCA course then you can check out this app "BCA - Course Programming" which is specially designed and developed for BCA students and is available on Google Play Store. 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

Please check for your eligibility to appear for the APSET entrance exam from the criteria mentioned below. APSET 2018 Eligibility:
APSET 2018 eligibility criteria which aspirants need to fulfil in order to be eligible to appear for the entrance exam is as mentioned below:
Candidates should have secured a minimum of 55% marks (without rounding off) in their Master's degree or equivalent exam from any university/college that is recognised by the UGC. Aspirants belonging to the reserved categories such as OBC (Non-Creamy Layer)/SC/ST/PwD are eligible to apply if they have secured a minimum of 50% aggregate in their Master's degree or equivalent exam. Aspirants who are appearing for their Master's degree final year exam and whose exam result is awaited can also apply for APSET exam. But such aspirants will be offered provisional admission and they need to submit their exam result details at the time of admission. Candidates who possess a Ph.D. degree and who have completed their Master's level examination by September 19, 1991 (irrespective of date when the result is declared) will be eligible for 5% relaxation in aggregate marks (that is, from 55% to 50%) for appearing in APSET exam. The official website informs that, Candidates are advised to appear in the subject of their post-graduation only. The candidates, whose post-graduation subject is not covered in the list of subjects may appear in a related subject. Age Limit: There is no upper age limit for candidates applying for the post of Assistant Professor.