1. My HD plan is to leave room clearing to the professionals and hold a safe position until they arrive. Do you really think you should get into room clearing?
Nope! Even with a trained group of guys in a stack going through that door is still called the 'fatal funnel' for a reason. Buy yourself---good luck!
Unless you have to go looking for family members I see no reason to do anything besides look for cover/concealment, orient your weapon on the rooms entryways, and call the police.