Engineering

See, these 2 courses are almost same in terms of everything but the only difference that is in the IT, you will get to know only 2 languages but in the CS you are supposed to be known more than 5 languages plus the placements, the placements of IGDTU is the best among both the options which you have mentioned above.

Employment of mechanical engineers is projected to grow 9 percent from 2016 to 2026, as fast as the average for all occupations. Mechanical engineers can work in many industries and on many types of projects. As a result, their growth rate will differ by the industries that employ them.

No, you have to pass that first.

If you ask for a straightforward answer, I'd say it makes a lot of sense to startup while in college. Mostly college allows.

Look the criteria for fees is different for different colleges, But you must have 50%+ to pursue CSE after Diploma for B.Tech.

Yes, anyway The weightage of 12th standard's percentage matters the most. A minimum of 50% is a must.

Best colleges for B.Tech after Diploma are-
Guru Nanak Dev Engineering College, Ludhiana
DAV Institute of Engineering and Technology, Jalandhar
Government College of Engineering, Pune
Guru Teg Bahadur, Delhi.