Yea WC put u into a different league i've just upgrade from a gigabyte 3d aurora to a lian li v2110 just so i can fit a quad rad inside the case (but then again im crazy as i thinking of trying to get a golftown (6core) to 4gig when it comes out).
But i would say after looking at ur case u either have two options
1 Corsair H50 (it will fit in ur case no problem the only problem u have is that u wont have a great amount of air moving through the pc so u will need a pci slot cooler (lian li do a great one))
or
2 Build a custom small pc wc kit and have the radiator mount on the back (however i would suggest at least a 360 rad with i7 for future proofing as sayso said)
The kit i would suggest would be
CPU EK supreme (so u can fit it to as many different type of socket mountings as possible)
GPU EK HD 4850 Acetal Full Cover I would say full cover is the only way to go really now, as the universal ones just wont be able to handle anything better than ur current gc (probably not even handle ur card). But then thats all down to the fact that were never only just adjusting the core speed of graphic cards anymore well its not our main aim. but u can add that at a later date.
Radiator I'm not sure on this really but for ur cpu u need 360+ (if ur gonna cool both cpu and gpu at some time) i would probably go for one that just fits ur situation (thin and long).
Res doesn't matter thats all about choice however u will have to have it fitted outside as u really don't have a lot of space in that case (apart from a bay res maybe)
Pump well as really there are only two pumps in this world the Laing DCC 18v (more powerful ddc version) and the laing D5 (gonna get the different part for it to use compression fittings on mine

) the D5 being the more powerful one.
Tubing pretty much 1/2 if u want chunky 3/8 if u want thin the advantages and disadvantages here are pretty simple.
really my feeling is if ur going to go wc go jump straight in the deep end. Just remenber its all about buying parts that will last so u will end up spending about 150 maybe 200 quid at least but if u take care of ur parts they can last u as many upgrades as u want. So its really do u want to buy something cheap but good now (that might not be so good later) or buy custom and when one part becomes crap it doesn't mean ur scrapping the whole thing. The benefit though about the H20 is u have watercooling running and ready in second doing it custom will take u days

.
it's ur call both are good options.
(Btw hehe this will be my first watercooled system built

but then strong with the force i am

)