I did for quite awhile after having pneumonia

I have found it helpful to use a rescue inhaler before exercising.

Yes I have used it while being on oxygen though I don't have to use it much

Sure. Using 02 ensures that your body gets the 02 it needs to make everything work the way it's supposed to. It doesn't do anything to "fix" your lungs, so you still need to take all medications and inhalers prescribed, including your rescue inhaler when you need it.

Yes, most definitely. However, since adding humidifier to my concentrator it seems to be not as necessary. This is a try it and see kind of thing!