You can use a welding tank for the O2 - I was told that welding grade and medical grade oxygen come from the same source - from what I remember the welding oxygen WAS manufactured (but no longer so) from a device that used oil as a lubricant for the engine that drove the device, hence there could be some low levels of oil in the oxygen.
Obviously welding oxygen does not require a prescription.
Welding tanks use a different fitting (that screws in the tank) Make sure you buy a tank that has a current rating (best to buy a new one)
The regulator is a pediatric regulator. but you need the CGA540 http://www.cramerdeckermedical.com/product.php?product_id=583
Please verify that my information is correct.