For your GPU block, check out this thread that I started a while back when I was asking the same question.
Which GPU Block?
AS for the NB block, personally you dont need to watercool it. A vantec Iceberg, ThermaTake Crystal Orb, or a BlueOrb is more than adequest to handle it. I am personally using the BlueOrb on my nForce2 NB and plan on hitting 200FSB. It does NOT add a lot of noise to the system.
Tubing on the GPU block can still be 3/8" and the rest of your system 1/2". Simply put a "T" line between your pump and your CPU block that uses 1/2" on the straight part and 3/8" on the "T" and run the 3/8" to the gpu block and then comeback to another "T" after the CPU block.
Go with the Dtek heatercore if you can afford it and have the room.
Good luck.