Stay away from HD or Lowes for steel rod. It is very expensive that way. As pointed out, check with the steel suppliers in your area. The sticks are 20' in length and most places will cut it in half for you for free. Also if you order in bulk, your price per stick comes down.
1/4" hot rolled is plenty sufficient for wireframe needs and is easily bent. Hot rolled is more stiff, but working with it is going to be a LOT more work.
With rope light, you will need to use zip ties rather than the clips talked about.