Serial numbers: Disk Management can't expose information in the console that the operating system can't see. So if you're not seeing serial numbers for some of your drives, perhaps the controller they're connected to doesn't make that information available, or the drives themselves don't (which would be odd, to be honest).
As for the distribution of data on your drives, it's completely normal.
One thing: I would recommend buying a couple of large drives, rather than trying to use a large number of smaller drives. 1 GB drives are pretty cheap these days...
I'm not on the WHS team, I just post a lot. :)