There is no minimum CGPA required to attempt GATE. But, if you qualify and apply for admission in masters program in any institute, then you must fulfill the CGPA/percentage criteria for that institute.It is not more than 60% or CGPA 6 in any IIT. IIT Delhi enforces 60% for general and 55% for OBC students. Most IITs just require a pass.
Number of past backlogs doesn't matter but you must make sure that before taking admission, you must not have any pending backlogs.
Regarding the GATE score that is required, different IITs come up with different opening and closing ranks for different different branches. You need to look at the past year GATE cutoffs given on the official GATE website for the details.
Hope you get to a good institute.
Regards
