A really nice challenge! I hope I can manage to join in.
For free resources I just copy what I wrote a few minutes ago in another topic::
You can use the free material library of Substance. There are over 1200 materials for free, and you can tweak them with the free Substance Player, then export the PBR maps and use them in Blender. All you need is a free account with Substance, you can use it to download the free Player as well as download the materials.
Substance Player (free without time limit)
Substance Share (over 1200 free materials)
For Substance Share: You can not use the “Smart Materials”, they don’t work with the Player. The Player needs the file format .sbsar, and those are under “materials”.
You can also find free .sbsar on CC0Textures.com
Good luck to everyone and happy blendering!
