FreeNAS Components Choice

I've already had some great help here, so wanted to ask a quite question about some components for a FreeNAS build? 

I would like to replace my three year old two bay synology with something with more power and space for streaming media, and storing backups from my Mac of mainly video and photo's I was considering another synology, something like a Synology DiskStation DS415+, which is around £750 dollars, so can I build something better for less money?

I saw the video about the as Rock C2750D4I, which looks perfect, but pretty expensive.  

So my ideal would be:

asRock C2750D4I


Fractal design node 304

2 x Seagate 4TB NAS HDD

Silverstone Strider ST45SF-G 450W 

My main need is for storing and serving photo's and video, and as a media server serving a Raspberry Pi running XBMC.  Which currently works fine with my old two bay synology. Its unlikely I will need to stream to multiple devices at one time, so I was wondering about the other 4 core Asrock board or what other cheaper options. 

I was hoping to be able to edit video directly from the NAS, but I think that may be difficult.  

Any component recommendations would be much appreciated. 

I'm also trying to get my head around link aggregation, I will need a managed switch, any budget recommendations?