1. Does it matter where you define the PortalShapes? The blender exporter puts it in the Light attribute block before the geometry. Would it also be possible to define the portals at the end of the file (or somewhere in the middle) together with the geometry?
Hey, the shapes need to be inside the light block.
However you could move that light block anywhere you want. (but the portalshapes have to remain in the lightblock)
On the other hand it's best to follow the luxblend output convention to make things transparent across platforms.
2. Can I make the shinymetal material completely matt (blind?)? I thought I could do that with the roughness value (0: clear reflection like metal, 1: matt reflection)
in theory a roughness of 1.0 will be pure lambertian. (however this is not always the case as you're still using microfacets)
it's also not a good idea performance wise, a lambertian brdf is much easier to compute.
a value of 0.0 should be perfectly specular. (however i'm not sure if this will work)
you might want to do 0.0000001 or something instead.