<font color="green"> Bob, do you have . . . </font>
YES to everything except air filtration, it is not needed. The room is one of our bedrooms, it has views outside, it has 'fire zones' that overlook much of the property including the driveway, it would be easy to escape the room but virtually impossible to access the room from outside.
The concept is to have a room where you can withstand a short duration attack and survive.
It must be escapable if the house is on fire, but while you need to be able to get out, it must be a difficult room to access from the outside. So a 2nd floor room is good, but only if you can't climb up onto a porch roof and walk in through a window! You need a chain fire escape ladder to get out or a real ladder to get in from outside.
Reinforced doors are a must, but the door frame is very important. A steel door set in a cheap door frame can be easily kicked open. A simple 'peephole' allows you to see the otherside of the door!
Having the room in a remote basement corner is a bad idea because unless you have lots of time while an intruder is beating down your front door then you and your family will have a hard time gettting to your safe room. A master bedroom is often in an ideal location in the house to become a safe room.
Phone & cellphone are a must.
A burglar alarm control panel inside the safe room is a must. It allows you to trigger the panic alarm, sirens, lights and auto dial for help. Lots of people put in alarms, they put in 1 or maybe 2 control panels. Most put them by their doors. That is fine, but if you are not by your door then you can't use your alarm. Have a panel in your safe room!
Plant beautiful thorn bushes under your windows. Barberry or rose bushes are great barrier plants. Very few people are stupid enough to crawl through a barberry bush to enter a window. If you have a tree that is close to the house then make it a Hawthrone tree, no human can climb one of those without ending up in the hospital and they have pretty spring blooms.
Like I said, it helps to think this stuff out.
Your house does not have to be a fortress, but you want the crooks to pass your house and go to the next one.