Does length matter ?

As @lak said, it matters if you want to sell them at some point.

Technically it matters but you might never hear s difference.

No difference. The near speed of light that electrons flow, means you wont be able to tell the difference, as also stated above the ohm load is  .0103. I found that as also stated coiling extra cable can cause issues of its own. I now use whatever length is esthetic to the install.

I had always heard that girth mattered more ... :)

Cables that low quality I doubt would Matter that much.