Probably, yes.
no it is not, but be aware that if your door is open,even a screen door, it is legal for them to just walk inside warrant or not
a cop and/or a judge out of his/her files
As is often the case with analyzing the legality of an action taken by a cop, whether the cop can "just open your door" depends on the specific circumstances. For example, a cop can open your door when the cop has observed a felony in progress by seeing it through a window. Or when the cop is in hot pursuit of someone the cop has observed entering the dwelling. Otherwise, the general rule is that the cop must have a warrant before entering a dwelling without permission, and even with a warrant the cop usually must knock first and request admission (although not if the cop has a "no knock" warrant).
A "cop-out" sheet is a form that a county jail provides to "inmates" that are currently incarcerated and have outstanding tickets or warrants to resolve. Once an inmate sends a "cop-out" sheet to the courthouse in which the ticket or warrant pertains to, that courthouse is "suppose" to call that inmate out to their court to resolve the matter at hand.
not if you let him search it
If the cop has a warrant or if he thinks you stole something or if the cop thinks you have a weapon in a place you are not suppose to have the weapon.
YES, BUT ONLY WITH YOUR CONSENT
Not if you have been convicted in a court of law for it. Otherwise, yes.
Anyone can be called to court to be a witness, including a resigned cop.
Walk into a cop shop and ask.
They must provide a judge with probable cause to do a search.
yes, but only after they arrest you