Here is the info to help you with the regulator and mask
This regulator will work on E tanks
https://www.amazon.com/EverOne-Oxygen-Regulator-Liters-Connection/dp/B07L9P7V55/ref=sr_1_fkmrnull_1_sspa?keywords=25plm+oxygen+regulator&qid=1554376658&s=gateway&sr=8-1-fkmrnull-spons&psc=1
This one will work on the M and M60 tanks
https://www.amazon.com/Oxygen-Regulator-Standard-Body-CGA540-protector/dp/B00BXRBJG8/ref=sr_1_fkmrnull_3_sspa?keywords=540+CGA+oxygen+regulator+0-25lpm&qid=1554376819&s=gateway&sr=8-3-fkmrnull-spons&psc=1
~OR~
wtfarley.com/Oxygen-Standard-Body-Click-Regulator-CGA-540
The mask can be found here
http://www.clusterheadaches.com/ccp8/index.php?app=ecom&ns=prodshow&ref=clustero2kit
As far as getting it covered by insurance, I have the issue of it costing way to much with insurance so I called around and told the oxygen companies that I will be paying out of pocket. It seems as if the insurance company actually sets the pricing and when I pay out of pocket the price is about half. I lucked out and have a company that will deliver the tanks to my house. I call in what I need and they come the next day. I am also chronic so I get this done all year round so I am not sure how that would work if I did not call in a order for 6 months of so.
I recommend calling as many companies as you can and tell them your paying out of pocket. Your other option is the welding route. You can read up on this on the site as well and get all the help you will need for that setup.