The full color logo is actually quite nice, it gives the impression that this piece was important to get right, and warranted more attention.

Different kind of tiles basically. Right now, there are only cobblestone (clean and dirty, but as Quenten mentioned, overgrown versions, things like tiles, loosely-fitted flagstone paving, etc.

Simple wooden bridges (whole, partially ruined, and ruined)

Tents/market stalls

More options for paving

Graveyard components (graves, tombs, mausoleums, fencing/gate). Both in good and broken down/overgrown versions.

Ships. Floating and wrecked.

Ruined keep/tower

Horses. Living, zombie and skeletal.

Wagons for said horses.

The displacement is based on a normal map. A normal map is basically a grid of vectors encoded using RGB values so you can store it as an image. The vector encoded in each pixel basically determines the direction for the displacement effect at that point.

The texture size tells CC3+ how to scale the texture you pick. If you want a single displacement image to cover the entirety of your map, set the effects units to map units, and the texture size to a value equal to the width (or height) of your map. If the value is lower than your map size, the displacement image will tile (which is usually the way you would use it).

The displacement amount is basically the strength of the effect, i.e how much the pixels should be displaced. May need som experimenting to get this right, and don't be afraid of going to pretty large values.