13'x15' loop and four cw80s or one zw?

One CW-80 will run the Polar Express with sufficient power feeds.

Start with four evenly spaced 12, 3, 6 & 9 o'clock and observe if the train slows anywhere. Then add a drop where it slows. (another note on FasTrack to follow)

Use 16awg for the feeds.  You don't really need terminal track as most all of FasTrack has terminals underneath. They may be beneficial floor layout, as they have the wire cut-out in the roadbed.

You can solder the leads to tabs underneath.

There are crimp terminal(.110 quick disconnect terminals) available at an auto store for a quick grab of enough. You could get the 16 primary wire there too.

The Polar Express only draws about two amps of the 5 available in a CW-80 set at full throttle for the LionChief version. The conventional is about the same and runs pretty fast at 7 volts.

leave your current set up as it is.

Assembling FasTrack for good continuity

The auto stores near you don't carry the terminals. How fast do you want to build? I can mail some to you or you can get them on ebay.

The others have covered it pretty well that the cw80 should be more than enough to run one engine.  use two in parallel if you end up needing more power

Mostly I wanted to note for folks, as far as I am aware, you can not use the wall packs with any other transformers as they supply DC power, not the AC conventional transformers do.

You can use as many transformers together as you like, or as many wall packs as you like, but not both to connected tracks.  ( including ones that might be bridged by a locomotive.