Good job, you survived, which is always the main focus.
Couple things. What if there had been two? Ever thought of a shotgun as a home defense? Mossberg 500 with 00 is like shooting 9 .38 rounds at once. Less likely that shaky hands are throwing off your aim, and more stopping force if his buddy that you didn't see comes charging around the door and you got to take a hip shot. Plus its a proven fact that the racking of a round will leave a yellow puddle where that burglar was standing.
Just a thought though.
If you're too cheap for an alarm, try that trick off conspiracy theory, upside down bottle on the door handle
Chain locks suck, thats why hotels stopped using them. But the ones they have with the knob and the loop of metal look pretty sound and easy to install yourself.
A radio or tv on probably isn't the best of ideas. Would you of heard the guy if the door was closed and a radio or tv on?
And as for the Castle law argument. Easy solution, kill the guy. Then you have one story told, yours. You can say the guy attacked you, pursued you, whatever. And he can't sue you. His family maybe, but he can't. And then you move. Because his gang banger esse's are coming after you for revenge. Maybe thats just paranoia... (Not being racist to mexicans I just liked the phrase gang banger esse's).