So what is your budget exactly? How many of those 3TB hard drives are you buying up front?
My immediate recommendation would be to buy
a cheaper motherboard. That ASRock is still an otherwise full-featured board but it would save you $50 over the ASUS. Spending money on a motherboard is fine, but a file server really doesn't need it.
My first file server I built was a complete piece of crap. I bought a $50 motherboard and $50 processor. It was several years ago now, but it only had four SATA ports and offered RAID 5 via the shitty GeForce 6150 chipset. I bought three 1TB drives (hot s**t at the time) which cost me twice the rest of the system (all of $200) and reused an old 160GB HDD I had as an OS drive, which left me relegated to using an IDE optical drive. But it worked. And reasonably well too.
The moral of this story is, don't focus on the motherboard. When you can afford to,
buy a dedicated RAID controller and slap it in a PCIe slot. That will give you much better performance overall and will allow for much better scalability. Just do a little research first to make sure what SATA/SAS port multiplier will work with whatever dedicated controller you end up purchasing. That way even you can easily split out a 4 or 8 port controller to support many more drives.
...
If I were you I'd stick it out with one 3TB drive for now. That way you at least get something that is functional and useful and - since you can afford it - sooner rather than later. If you need more storage in the interim, buy an external drive and hook that up.
Then save up for a dedicated controller and four 3/4TB hard drives. In RAID 5 that will get you 8-11TiB of actual storage that is protected against failure, as well as something that is expandable that you can easily add drives to in the future.
One thing I would look into if I were you though is if FreeNAS has support for dedicated RAID controllers. I'm sure it offers some level of driver support, but exactly what it supports could be questionable. Check it out at least. You may be forced into a different OS depending on the card.
100
