QGIS 3.0.0-3 should fix the non-working GRASS problem. The key was my adding the “3” to the app name with a space, the GRASS internals didn’t like that. So I removed the space – it’s now QGIS3.app. The installer removes the contents of the original QGIS 3.app, but not the app folder itself, so you need to delete that from your Applications folder.
It also looks like the rebuild fixed the missing SAGA processing tools.
On to figuring out why GDAL tools do not work…