We’re unable to pull in smart crates, because they are actually searches that Serato makes and we don’t have access to that info unfortunately. The workaround would be to copy all tracks in a smart crate over to a regular crate and then import it, then just keep it updated everytime you import new tracks.
As for the import time - large databases will take longer to import. We are looking into ways to reduce this however we can not promise a date for this.