I think it's best to check with the company that will be refilling your tanks. In my area, gas suppliers will only fill their own tanks. When I need a refill, I simply exchange my empty for a full tank. This way I need not worry about the static pressure test, which, as you said, needs to be done on some sort of schedule. I think it's something like every 10 years. If you buy from a private owner, he should have some sort of title or lease contract that can be transferred to you.

Good luck!