Yes, just about: 3.1 billion base pairs for humans vs. 2.7 billion base pairs for mice. Most of that is identical between the two genomes.
I think there are 3 billion polypeptides in human DNA so that would seem like a lot more than needed to make a mouse.
As you say, but the microbe Amoeba dubia has a genome that's 670 billion base pairs long, some 200 times what we have at our disposal. Who's to say what's needed?
I don't understand your statement? Do you think that an amoeba is 200 times more complex than a man? If your 670 billion is correct then that sure implies that a lot is not used in the amoeba. In either I would hope that we agree that the order of complexity is amoeba, mouse, man though some of the processes are probably pretty similar within the mouse and the man.