Coiling ac wire around iron rod bad or good?
Heat could still be an issue. The main problem with wrapping wire around something is that you are decreasing the surface area. This leads to increased temperatures. However, if the cable is thick enough and the current is not too high, the temperature rise should be acceptable. I would guess that powering a 500W power supply from mains voltage in the described setup should be fine. To be safe, check if the cables are getting hot under full load.
Another point to consider is that you are building an inductor by wrapping wire around an Iron rod. The inductance is roughly twice as high compared to wrapping it around a non-magnetic material. But in your case with 5 m of wire, the inductance will still be quite low and will not have any meaningful effect at mains frequency.
Wrapping the wire around the metal rod will not affect your electrical bill in a noticeable way.
If the insulation of the wire is intact, there should be no risk of electric shock. I would still suggest looking for a shorter wire and not wrapping it around the metallic table leg, even if it is only safety relevant in unlikely scenarios.