How much tile images do you need

More tile images you have in library, better mosaic you'll get.

If you don't mind to use a heavy color correction you may use about 100 or 200 images.

If you want to make a better mosaic with less color correction from the same limited number of tiles you should cut and crop these images as said here. It will give you 500 - 1000 smaller tiles that usually is enough for a quite nice work.

To render mosaic with default settings - Repeat = <Auto>  and Distance=<6> you had to have at least 144 different tiles in your library. If you have less - you'll get <Not enough tiles> error message and in that case you had to either add tiles into library either decrease the Distance setting.

Here are few more reference numbers:
Distance: 1  -  requires  4 images in library
Distance: 2  -  requires  16 images in library
Distance: 3  -  requires  36 images in library
Distance: 4  -  requires  64 images in library
Distance: 5  -  requires  100 images in library
Distance: 6  -  requires  144 images in library

Or you may use this formula:
Distance: N  -  requires  N*N*4 images in library

Mazaika - (C) 2000-2018 by Boris A. Glazer.