I run 2 3TB Hitachis in an external non-raid enclosure and use synctoy to do manual backups every once in a while.
Needed more storage for my HD movies and didn't want to clog up the internals of my system, so i opted for an external enclosure.
Didn't look for an enclosure that had hardware raid as I didn't want to be tied down to that same enclosure should my current one fail on me.
why not you get this to begin with?
http://www.frozencpu.com/products/17638/ex-wat-229/XSPC_Raystorm_RX240_Universal_CPU_Water_Cooling_Kit_w_D5_Variant_Pump_Included_and_Free_Dead-Water.html?tl=g30c83s137
then you wont have to go through the trouble to upgrade the pump in future.
unless $$ is a big problem, i suggest you get the D5 pump right from the start. It's more cost effective than upgrading the xspc750 to a D5 in future
for low noise + best performance, go for low FPI, THICK rads with low RPM fans.
if you have the space for push/pull, you can go for even lower RPM fans to get similar performance :)