You can easily get a pcie card to add 4 more sata ports. That's what I plan on doing. I'm not using a dvd drive or anything with my server so I plan on filling the box up with 7 drives total. Like you, my mobo only has 4 SATA ports so I'll need an expansion card.
Does anyone have a preference on these pci-e cards?
This seems like a question I should already know the answer to but can you throw pci cards into pci-e slot?