Cheap datacruncher, opinions on this spec?

Hi, I'm in search of:

A cheap, future proof data-crunching computer for statistical work (at home). This includes storage and backup of large datasets. I have built only once before, some 6-7 years ago..

Need:
-Large amounts of memory (now just 4-8Gb but must have the option to expand)
-Processor speed per se not the main point, but multicores will be useful.
-Trustworthy core components
-It has to be cheap (I'd like to go under £300, but potentially willing to wait to save more and wait prices go down)
-I think USB 3.0 would be good for fast external backups.
-Linux supported (well pretty much everything is these days)

What I don't need:
-Graphics. Onboard graphics or a low end card ok. The box may end up being only for remote connections..
-Anything related to gaming.
-Probably don't need sound.

I'd like to have comments on the spec here, possible alterations, or things I haven't thought of. Prices are in UK pounds..

Motherboard:
1xUSB3, 16Gb, ATX
Asrock 770 Extreme3 Socket AM3 8 Channel Audio ATX Motherboard
Ebuyer £67.13 (http://www.ebuyer.com/product/204541)
(Cheapest USB3.0 board with 16Gb memory support and good reports from Linux users)

Processor:
AMD Athlon II X4 640 Socket AM3 3GHz 2MB L2 Cache Retail Boxed Processor
Ebuyer £77.12 (http://www.ebuyer.com/product/242140)

Memory:
Corsair 4GB DDR3 1333MHz Non-ECC (9-9-9-24) 1.50V - Core I7, Core I5 And Core 2/AMD Phenom Ii - *Dual Channel
Ebuyer £52.29 (http://www.ebuyer.com/product/237100)
(I wanted 4Gb sticks to keep upgrades cheap, start with one)

Heatsink & Fan:
Arctic Cooling Freezer 7 Pro rev 2 Socket 775, 1156, 1366, AM2, AM3 Heatpipe CPU Cooler
Ebuyer £14.75 (http://www.ebuyer.com/product/176157)
(Cooling is an area I'm pretty ignorant, so went for something cheap)

Disk:
Western Digital WD5000AAKS 500GB SATAII 7200RPM 16MB Cache - OEM Caviar Blue
Ebuyer £31.35 (http://www.ebuyer.com/product/124228)

Case:
Planning to use a 10-year old cheapo case I have at home. Any point in getting a good new case?

PSU:
Need to buy a 400W PSU (I think it should be enough)

Other things
-External USB3 backup disk... (not urgent)
-SSD drive? (Not at all sure I need it)


So now it's £242.63, excluding PSU, Case and other things. Something I don't know much about is what would be the benefits of a higher end board, and what would I get with extra money. Also the issues of case, PSU and cooling are difficult to me - I'm unsure about what money will buy for me. I'm pretty sure that Athlon II X4 is the right processor for me. It's great value for money and I doubt I need the L3 cache of Phenoms...

Any opinions appreciated!