Here are some better prices on the pumps. The flow rate of the one you found will be more than sufficient.
Multiple radiators are not necessary. Go for 1 360mm radiator. The temperature of the water will not change significantly throughout the loop.
Cooling the NB with water is a worthwhile thing now. This is because in order to get the Core 2 to its maximum potential, you need more than 1.85V in the NB.