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

Yes. Here are some general tips for texture files that you upload to Nira:

• Texture width and height dimensions should be a power of two. For example, if you upload 16K textures, the texture file dimensions should be exactly 16384 x 16384. 
  For reference, the correct power of two width and height dimensions for textures should be:
  • 4096 x 4096 (4K)
  • 8192 x 8192 (8K)
  • 16384 x 16384 (16K)
  • 32768 x 32768 (32K)
• Use 16K or 32K textures, whenever possible. Using smaller textures (e.g. 4K or 8K) results in more files, which will take longer to load.