Fir the first, the part in parenthesis, I'm not sure what you mean here.
But DrivePool is entirely folder based duplication. And more or less "random" about where the files are placed.
As for controlling the location: http://community.covecube.com/index.php?/topic/208-stablebit-drivepool-controlling-folder-placement/
But in the meanwhile, you could set up two Pools. One on internal disks, and one on external USB drives. And then use Free File Sync, Always Sync or other such utilities to copy the files to the "external" pool.
