After I-485 approval what?

[pmpforgc]

Once your I-485 is approved and GC received -

1) Is it neccessary to get stamped in passport, even if you get actual green cards?

(2) What happens to your I-94's that you currently have, if you dont go for stamping?

(3) How long one needs to stay with sposoring employer before changing job (after getting actual GC)?

Hope guidance from experienced members

thanks