need you opinion please

[MrToad]

is this controller good it holds 20 watts per channel:
Sunbeam 4 Channel Rheobus

There's plenty of people on this forum that use it, never heard of any complains.

However, IMHO the best way to make appropriate choices is to research first how things work.

This page is a good start.

Regarding your second question, I don't have an answer. You haven't specified which NB, SB or Mosfet blocks you are going to use. In fact AFAIK there's no 780i NB block yet, and I have a feeling none of the existing ones fit.

Have a play with Martin's flow rate estimator (it's in the stickies) using existing components, and judge the flow for yourself. Then calculate how much heat your components dump in the loop, and compare it to the heat dissipation capabilities of your rads for your chosen fans and given flow. Your guess is as good as mine.