I have learned tons by reading here over the years...and finally went with a 2X120mm radiator in my latest build:
That is the preliminary fill/leak test, and then I did some more modding and wiring to finish it:
I never got to purchase the real premium low rpm fans, but with two Vantec Stealth on the Radiator, pull only, no shroud, its very quiet.
I put the DD-D5 pump down below on the bottom level, behind the opticals and next to the PSU. The first week had some whooshing sounds as the microbubbles worked out, but now I can't hear any pump sounds.
I think pump placement is part of it, mounting (on industrial velcro), and I could probably help it even more with some rubber feet on my case.