Nelie,
I can't help much with your first two questions -- I think masks weren't generally in use when I had radiation, and I never had a PEG tube.
On your third point, your teeth and gums will definitely need extra attention for the rest of your life following radiation. I have routine cleanings every 2-3 months, and I see an oral surgeon or a periodontist (both of whom are very aware of my cancer history) for anything that might require more specialized work and additional caution. That said, I haven't had to have HBO for anything yet, and I've had a number of fillings, crowns, gum grafts, etc. in the past 15 years -- all with no complications.
Cathy