Are there ideal dimensions (width and height) for texture files?

Yes. 

Texture width and height dimensions should be a power of two.

• For example, if you upload a 16K texture, the texture file dimensions should be exactly 16384 x 16384.  Here are several examples of correct power of two texture width and height dimensions:
  • 2048 x 2048 (2K)
  • 4096 x 4096 (4K)
  • 8192 x 8192 (8K)
  • 16384 x 16384 (16K)
  • 32768 x 32768 (32K)
  • 16384 x 4096 (Different width and height is fine, as long as they are both a power of two)

Use large 16K or 32K textures, whenever possible. Using multiple smaller textures (e.g. 4K or 8K) results in more files, which will take longer to load.

New Feature Update (2023-05-25):

Automatic texture upscaling

Any texture image uploaded on or after 2023-05-25 that does not use power of two width and height dimensions will be automatically upscaled to the next power of two. For example, if you upload a 17000 x 17000 texture, it will be automatically upscaled to 32768 x 32768. This automatic upscaling does produce more texture data for our servers to store and load, which can effect how much you may pay for the asset. For this reason, it is still best to configure your application to save or export power of two textures whenever it is practical for you.