回複：basic question need answer

To apply a green card, my approach is PERM/Labor Certificate--->I140--->I485--->? Upon what step I can say I got the so-called greencard?

After your 485 is approved.

Is this only one of approaches that lead to green card, if yes, what's special about it?
No. There are other ways to apply GC.

For EB1 and NIW, you don't need the PERM/Labor Certificate.

Upon when I can be free---change employer without any restriction? I picked up from somewhere if I applied green card with this approach, I will stuck with the current employer forever, is that true?

After 140 approved and 485 filed for 180+ days, you can changed employer, but must do the similar kind of job.

Thanks for any input. This PERM thing has been bothering me for quite some time, I really want to clarify things