Yes! All the models are manifold, have uniform scale and have no overlapping or intersecting parts. Just apply all the modifiers in the stack and you can export any model to your favourite format.
I have baked all the PBR maps in 16bit 4K x 4K resolution and its almost 200 megabytes now. There is no place on this site to upload it, so contact me for a link to download the maps.
Yes, except some slight differences with the roughness of stained brass and stained silver.
Yes! I tested all the models and materials in 2.8 and haven't noticed any issues.