It's an excellent question, and one I'm not sure has an easy answer. As I repeated in the thread on modified weapons, the cases are fact specific.
The first thing to look at in answering your question, is what is your "home". The law has always recognized that your "home" is more than the building where your bed is. The common law has the concept of "curtilege" which is the fenced in area that you kept your sheep in around the building that had your bed in it. The term is still used, and the concept recognized in 4th Amendment search and seizure analysis. There is a recent SCOTUS case finding that a motorcycle in a driveway with a tarp over it was part of the "curtilege" and not subject to warrantless search. So you do not have to allow them in to enter your house.
Looking further at the Georgia law on self defense, deadly force is allowed TO PREVENT the commission of a forcible felony. You don't have to STOP a forcible felony, although that's the way most SD cases play out. Burglary is a forcible felony. The law does not define at what point you must begin to stop its commission.
In the present case, the homeowner had an aged mother in the house. i believe this information was posted on the property. Turning your question around, seeing 5 hooded persons carrying handguns at 4 a.m. approaching your house, do you have to allow them to enter it before engaging them in a gun fight, and very possibly endangering your mother in any number of ways. Using the "reasonable person" I think the answer is "no".
You are perfectly within your rights to arm yourself and accost any one at any time on your property and inquire as to their purpose. Given the times we live in, it would be hard to find a "reasonable person" who would fault the homeowner for arming himself before making this inquiry. To me, it's significant that he didn't "fort up" in the house and ambush them. That would be questionable conduct.
He didn't get to make his inquiry because the masked men started shooting at him. All accounts agree on this. One neighbor said several pistol shots were fired before the rifle was fired.
Once the masked guys start shooting, it becomes completely irrelevant whether the homeowner is in his house, his front yard, or the Wal-Marty parking lot - he has the right to defend himself.
So to answer your first question, yes, it's o.k. to shoot people on your property IF THE CIRCUMSTANCES WARRANT IT. In Georgia, simple trespass is not a crime, so if that's all they are doing, you can't shoot them. Stealing property is not a forcible felony, so the kid stealing your lawnmower or even your car is not a threat that justifies shooting him.
Your second question is if he went out after them it's different, and the answer is "not much". The biggest difference is that a person burglarizing an inhabited building is presumed to present a threat to the occupants, and deadly force can be used to end the burglary. The fact that he only wanted to steal your big screen TV is irrelevant. BUT THIS IS IMPORTANT, if he has stolen your TV and is retreating/leaving you cannot use deadly force.
And to answer your 3rd question, this incident at some level is a "stand your ground" case, but it is a straight up SD case, and has been for 250 years in Georgia, the "stand your ground" law adds absolutely no protection to the homeowner that did not exist before the law was passed. In some states, arguably, the homeowner would have had a duty to retreat when the hoods started shooting and so "stand your ground" may offer some protection for the homeowner. That's a very murky subject even in those states, and fortunately we don't have to worry about it.
