NAS build/Media center, need some input

so, I'm in the process of building a NAS / Media center PC, with the purpose of offloading some tasks from my stationary, and I'm curious as to what the best parts are. I'm not sure if I should go with an AMD or intel chipset, since I have literally no experience or knowledge what so ever of building a NAS.
I also wan't to know whether I should get a cheap SSD for the boot drive or just use the HDD's.

I do want a somewhat nice processor since this will be running plex, BTsync etc. I will also be messing around with some other software just to see how it works and potentially start using it permanently. On the other hand I have no idea how much processing power this will even use, so I can't tell how expensive my processor should be.

HDD wise I'm thinking any 3 TB HDD will do, going mostly for cost efficiency so the amount of storage isn't all that important BUT this thing will eventually be keeping several TiB's of data, (roughly 500GB prepared to load onto it already)
As for MoBo and Case I want as much storage as possible, as long as the price is reasonable, I may change the chipset for the purpose of getting more SATA ports, but first I'd need a case with more storage slots than the one I'm considering right now.(Fractal R5)
on a side note, I would like to get a MoBo with more SATA ports since I have a HDD drive cage from the fractal R2 which I hope to be able to use in this NAS thing later.

current parts in consideration: http://pcpartpicker.com/p/XZ8gmG
EDIT; note; not listed is an adata sx900 that may or may not work.
Definitely Wont work.

for suggestions on other parts go check http://komplett.no but keep in mind that the prices on that site are basically irrelevant, as long as it's on there and it doesn't cost too much more than what I've selected already. Also note that the PSU will be salvaged from a PC that needs a higher wattage and is therefore more or less locked in.

my budget for this build is roughly $700


Also I want some tips on OS and software (off topic I know), I will probably be using freeNAS but, if you think you have a better option shoot for it.

I'm not a expert but I can tell you what I know from what I built,...

I'll just jump to the end first, the OS, you really need to decide on the OS before picking your hardware because an OS like FreeNass can run on a minimal CPU (likes more cores than Ghz) but loves RAM, in fact the more RAM the better.

I built a media server using FreeNas several months ago and used a Intel Atom processor (2550 - 2.4ghz) and 16gb of RAM, running FreeNas 9.3, 5 WD 3TB reds in a Z2 configuration giving me a little over 7TB of storage and redundancy in case one of the drives fails, ZFS is a great filesystem. This box runs headless in a rack and streams content to all of our TVs which either have WD live boxes or much older Asus oPlay boxes, we use Plex as a front end which also works great.

The board I used was a http://www.asrockrack.com/general/productdetail.asp?Model=C2550D4I#Specifications I used this board because it has plenty of SATA ports, uses standard ram, and has dual Intel gigabit nics, very low power usage which is important in a box that will run 24/7/356, I think my total wattage under load was about 60-70w and was around 55w at idle. Freenas will install to a USB thumb drive and as long as your MB will boot from USB you good to go, you wouldn't want to install FreeNas to a harddrive because it will take up every bit of it regardless of the size of the disk, a 8gb thumb drive is more than enough space to hold the OS.

What I'm basically trying to show you is that you don't need high end hardware to run Freenas or a media server, we can stream to 4 or 5 devices simultaneously and never even get close to 5% CPU/system load on a gigabit network....the little atom CPU is more than enough to handle everything we can throw at it, the box actually does more than house and stream content it also has programs installed that are content aggregators, the box also runs a Samba server for windows shares and remote file maintenance.

Anyway there is lots of info around the net I'd suggest you look at http://www.freenas.org/
You may also find this video of interest. https://www.youtube.com/watch?v=p4gm6sCJXQc

Hope this helps you in some way....