So if we can somehow preserve the signal and make it go round and round, can we get long term storage out of nothing?
Not a scientist, but I assume the signal would degrade or mutate over time due to space radiation and other radio waves.
This is possible but you'd have to deploy it right by a black hole: https://en.wikipedia.org/wiki/Photon_sphere
You're still storing your data in the same EM field, just in a slightly different non-inertial reference frame.
"Nothing" is a funny name for an interplanetary communication network.