I have a few questions, first from where do you drain the system, by the fill tube (i.e. topping down the case) ?
yea tip the case over, drains nicely
Next, don't you fear a leak springing from the tubing->pump attachment since the pump is suspended after the tubing ?
not really, I've used a molecular bond plumbing adhesive to do the in-line pump mod, the barbs aren't coming off

, they'll be clamped in the final install (pics we're from the overnight leak test) the pvc tubing should easily be able to support the weight of the pump, it's pretty light.
Finally, does this HDD cooling system allow noise insulation -> is it efficient enough ? Did you take any measurements (through S.M.A.R.T. function or with a temp probe) ?
The system isn't together yet so I don't know, though the rest of the case will be sound damped, I'll see if the the HDD's are noticable when it's all together.