Building a budget NAS?

Hi all,

I’ve recently started thinking if setting up a basic home server to use as a NAS for emby for use over local network.

I’ve read the budget build but still have a few questions as it’s my first server and Nas setup I will be doing so I may get a few things wrong.

I’m thinking of using a dell t100v2 3.1ghz Xeon processor, 12gb of ram, standard psu, graphics etc.
Wanting to add 3 or possibly 4 3tb wd green caviar HDDs, using one drive for parity, so data on other discs is shared over all the drives.
I’m wanting to run unraid so should one drive begin to fail I can swap the dieing drive to a new one and not lose my media/data.
I’m thinking of using unraid for my 0S
The questions I have are:
Is the above spec okay or is something likely to be an issue?
Will I need a raid card?
Do I need an SSD for cache ?

As I say I’m new to this so if I have made an obvious error I would sooner ask and know now before I start buying things. It will only be Nas really over local network

Thanks