JEE

The admission process for BTech is based on qualifying entrance exams such as JEE Main/ SUAT. Candidates with JEE Main rank less than 3,00,000 or Uttar Pradesh State Entrance Examination (UPSEE) rank less than 50,000 are exempted from Sharda University Admission Test (SUAT).

The selection process for B.Sc programs at SP Jain School of Global Management involves several stages, including an entrance test, aptitude test, and interview. the institution accepts various entrance exam scores, such as JEE Main, SAT India, and SPJET. 
It is recommended to visit the official website of SP Jain School of Global Management or contact the admissions office directly for more up-to-date information regarding JEE cutoff.

Yes as the eligibility criterion is to have 50% in 10+2 in pcm from any recognised board. 
You are now eligible but you still need to crack the entrance exam or get admission through merit list.

You need to give the JEE exam. 

Yes, probably. Although the cutoff percentile for getting an admission in CUJ varies from year to year, it is safe to say that 75 percentile in JEE is sufficient in most of the cases, as the cutoff never exceeded above this value, one can check the previous year cutoff trends in the official website of the college itself.

The selection process for B.Tech at Northcap University is based on the JEE Main score. Candidates must have studied Physics and Mathematics as mandatory subjects along with one of the Chemistry, Biology, Biotechnology, or Technical Vocational Subjects. There is no fixed minimum score required in Class 12 for JEE Main, but candidates must fulfill the eligibility criteria specified by NTA. As per the JEE Main eligibility criteria, students can appear in the JEE Main exam for three consecutive years.

Based on your question, on 140 your percentile will lie between 97-98 and your rank will be around 24,000-35,000. Given that you're a general category male student, CSE at any decent NITs will not be available to you, even if you are a home state student. However, stats and your chances may differ if you are from category or are a female student. 

For appearing in JEE exam you don't need a very high computer knoweldge. Although JEE is in CBT (computer based test) mode, but you only have to select your answers in multiple choice questions. 

All the very best!

To get admission in a decent NIT, regardless of branch preferences, a percentile score of 97 is optimistic for general category students. However marks required for 97 percentile differs on the basis of the hardness of the shift and relative performance of other students. A score of 130+ is considered target for a hard exam paper whereas 145 for a easier one. All the very best!