Adual loop can make things a bit complicated, but if youve got the space, and moent to do it, go for it. It'll give you a few extra Mhz, but in my opinion not worth the effort (or investment).
I think you may be able to push for a dual thermochill rad, but a triple rad would be fine for sure.
The swiftech kits are highly recommended, but if you want to go custom (which you probably will have to coz of the rig) some sound choices are:
CPU block - TDX, RBX, Storm, Apogee, Nexxxos XP (maybe AquaComputers stuff but dont know enough about them)
GPU blocks - DD sli blocks, Nexxxos GFX block, e2k (sp?)
PUMP - D5/MCP655, D4/MCP650, DCC/MCP355, DCC+, Eheim HPPS (not recomending the other eheim because of the need for a relay CAN complicate things, but they are excellent pumps aswell)
Tubing - Tygon/DD/Clearflex/Masterclear.... you may want to consider wether you want to go large bore (1/2'' or 3/8'') or small bore (8mm n 6mm id tubing).
Radiators - Thermochill (my personal faveorite), Swiftech, Blick Ice Pro (for queiter operation) / Extreme (higher performance with hi RPM fans) / GT (suppose to be great, but not read any reviews).
Liquid - De-ionized water with additive (zerex, water watter), or soomething like MCT-5/40 or fluid XP)
Remember to keep barb size the same throughout in the lopp, and tap water is a no no
If this mean nothing to you, then some reading up is dude
