Hi,
If cost not an issue here, then best to get one of the raid constoller (yes, I know we do not need raid with whs), the point to get ports, and in good speed as well.
I recommended something like
Areca or
3ware card, sure I will go with pci-e or pci-x (for speed matters), but since the option with pci, then fine.
I put one of these card like 8 or 12 ports, let for now, say the 8-ports pci one, then I would buy either 1tb or 750gb hard disks (depended on the cost you want to go by at this point).
The above controller as we will just use them for none-raid, even so, we will get way better speed, way better insure for our data, from many years with data storage issue, I find connecting your hard disk with good controller, give better result for hard disk MTBF issue than to use the MB ports (personal view tho).
Again, it depended how you see it:
1 - Option as, just replace the hard disks with bigger one, from 250, and 400 to 1tb or 750gb.
2 - Invest in better controller, and add bigger or more hard disk.
3 - Cheap controller and then add more drive etc.
My best.