Backing up to external USB drive first. Yes, that will be possible. The setup is pretty straightforward, you just need to correctly specify the path to the storage destination after the data has been transferred and synchronize the repository via tools > options > repository after you finished transferring the data to its final destination.
As for slow image-based backups to network share - that is a known rare issue. Target release for the fix is version 6.0.1, which is scheduled for release in October.