Which gives a better track to become a professor after completing B.Tech and preparing for GATE- M.Tech followed by PhD or M.Sc?

No, there is no subject-wise cutoff mark for GATE exam. The scores along with minimum-qualifying cutoff will be released (category-wise) along with normalised score. 

• GATE Marks out of 100
• GATE Scores out of 1000

A GATE score of 550 in mechanical engineering will fetch you a rank range of 1500 - 3000. Students with this GATE score range can opt for M.Tech at NIT Calicut, NIT Trichy, etc. 

Based on the question paper difficulty level of GATE CS 1 and CS2, it is expected that the normalisation will not be more than +-4 to 5 marks. GATE CSE paper was moderate to tough. The result will be declared on March 19. Candidates can check their qualifying status at GOAPS portal using their enrol

Yes, with 50 marks in the GATE exam candidates can get admission to few IITs and NITs as well. 

For top NITs, the safe score in GATE will be roughly around 650 - 750 scores. However, it also depends on other factors, such as category, past year trends, etc.