a) Rads specifically designed for Water Cooling are best for the job. Make sure they are Cu/Brass.
b) Your heatercore would outperform any Al rad.
b) I have never witnessed galvanic corrosion. I have Al block with brass inlets and a Cu/Brass Heatercore without coolant. Furthermore, its tap water (actually boiled to 100C for 30mins
)
If you are still concerned about corrosion, just increase the coolant ratio.
c) If you are looking for performance 120mm FANs, check out NIDEC.
http://www.nidec.com/fans.html#
They have 120mm @ 225CFM 12V. They have a contract with Intel ® so my guess is that they are the best. They however do not look 'cool'.