tonearm cable, do you need one?

Not unless there is something wrong with what you're currently using. If you do require a new cable and want the best quality - search ebay and other sites for "made in Japan." 

Some IC's may be noisier than others due to build(shielding) If you choose to not use phono   cables, just use a piece of wire  for the ground(table to phonostage). You may not even need it. My VPI doesn't depending on cart used for whatever reason.

Zu Audio Phono cables with ground wire are excellent!
You need shielded phono cable.
Read more here.

And on ebay you can find their auctions for Mission Phono RCA cables with starting price at $1, normally goes for $80-100 on those auctions. They are great for the money! 

If your phono cable does not have this third ground wire then you can still try it, and if you hear some hum then you can’t use it without separate ground wire, just try it.