I agree with the first step being to call 911.
Looks like everyone forgot to give the LEOs your OWN physical description, including your clothes. Depending on local climate, you may or may not wish to tell them that you, the good-guy homeowner and crime victim, are armed. Describe the BG as much as possible as well.
Portable phone is good. Keep it with you. Keep the line open if they let you.
I would choose the best-situated doorway or sliding window, and give the command to "Freeze, I have a gun." Assess compliance. If he tries to flee, shoot only if his exit from the truck takes him/her/it towards my position.
If compliant, order him to place his hands on the steering wheel and stay put.
I would probably wait to give the first verbal command until a minute or two after dialing 911. Wait for a time when his/her/its head is in sight. At any of these times, the perpetrator may be about to leave. The rationale for the command is to effect a citizen's arrest and detain the perp.
I would also stay 3 or more feet away from the door or window at all times. Most residential walls and especially doors provide only concealment and no cover. Watch the perp's eyes for attempts to contact accomplices. Command the perp to keep eyes forward. If you command him to keep his eyes down, you will lose the intelligence value of seeing something catch his eye!
I would also douse all lights inside and any outside which could silhouette me, as I have done in previous night-noise investigations.