Remember hotels are actually extending you credit when you checkin so they are protecting themself by authorizing the cost of the unpaid portion of room and tax for the entire stay plus a small amount for incidentials....since your stay is already paid for they will only authorize the incidental amount (this is all computer driven and not a manual process)

1) no
2) yes but only by paying cash and not providing a credit/debit card at check in but this will result in you not being able to charge any items to your room
3) yes
4) see my the reasoning above