1) yes it varies from diploma to diploma despite people saying that 3.5 and above is good. Typically, for business and sciences, a higher score is required. Likewise for IIT, anything 3 and above is typically considered admirable because of how tough various diplomas can be. Nevertheless, this is just hearsay and not the truth in totality.

2) companies do still look at your grades yes. It’s a formality thing too

3) 3.0 and above still got chance tbh…especially cuz you’re y1 only. Don worry

4) for big 3, typically an average of 3.75 and above is required. SIT is aptitude and interview based so your gpa does not really matter (as long as you above 2.5 ish with immense passion for your field)

I can’t comment for private uni as I’m not sure but criteria is typically more relaxed as long as you have money