My question is what can I add to this to create something to play SWToR on (if anything) just until I have the money to get something better. I really would like to re-use some of the parts I get for a Sandy Bridge build down the line if possible. If not then cheapness is the key.
The PCIe cards are backwards compatible. So the 6870 should work fine in the single 16x PCIe slot you have.
And considering even the fastests cards are barely starting to hit the limits of 8x PCIe gen2 which is the same as you 16x PCIe gen1 you should be ok.
Do take into account that the 6870 cards are quite long, so make sure there is enough space in the case you do end up selecting.
However the 6850 is not a bad option if you can find it for considerably less money, should make it easier on the PSU as well.
Just make sure you PSU is up to the task to running the 6870. A good 450W-500W unit will do fine.
I wouldn't touch the one that comes with the case you listed with a 10 foot pole, but it 'might' do the trick.
Seasonic, XFX, Corsair, Silverstone and antec all have good units in the desired range, but they do cost about 40£+
XFX Core Pro 650W £66.53 being about the top end you should be looking at pricewise.