those vid cards will only go up that high when under laod or else stay cooler when not in use, and the top 2 cards will get hot becouse the 3'rd is running physx and dont have that mutch load on it.
get a pump/res combo ( personaly i prefer tube res before bay res option ).
you need a case that have loads of rad space in it. ( 900D is a good one but a huge ass case )
think 2x 120 fan slot per card for radiator space cooling.
i would recommend a fan controller for the fans. ( one whit lcd monitor on to monitor temps on water ) for a inline temp probe.
like this one ->
http://shop.aquacomputer.de/images/product_images/popup_images/53067.jpgfans i would get ones whit high MMH2O ( Static Pressure and not CFM ) and low start voltage. ( 3 or 4 pin up to you ).
if you are going to colored coolant i would go for colored tubing before the coolant, its a pain to get out and clean later.
get a drain option on the lowest part of the loop so reduce spillage in case leakage and when you are going to change coolant ( every 1-2 year ).
clean rads before instaling to get out resedue from machining and production so the resedue dont destroy the impellars on the pump.
use deionised water ( battery water ( not the acid one ) ) think you can get gallon bottles for a cheep penny in a store of some kind.
do you have the option to mount a fan on the door of the current case you have now?
if so mount one to help cool down the vid cards.
fans, front in and roof and back out ( way of the heat since it goes UP ).
a waterloop WILL set you back close to $1000 or more so think about it before going that way.
as posted up there you NEED the case for it and you WILL void warranty when doing it.