Large no. of tiles when using Tile Generator

Hello all,

I'm trying out Designer and have watched many tutorials and started my first material.  In most tutorials where the tile generator is used the number of tiles is usually 10x10 or lower.

For a mosaic material I need at least 80x80 or more, as the mosaic is small (around 25x25mm) so if I generate a 10x10 tile then it will only cover a small area and the tiling will be obvious.

I noticed that if I start small (say 6x6) and then increase that at the end the scale of all the grunge I apply then needs to be adjusted - pretty much starting from scratch...

So I increased the tile generator settings to 100x100 but it's quite difficult to see what I'm doing at 2k resolution and ideally I'd like to work at at least 4k, though 8k would be ideal.

So are there any workflow changes I should be aware of?  Can I crop the work area so that even though I'd like a 100x100 material I only work on a 6x6 area?

Am I even going about this the right way?

Sorry for the noob questions