Hello,
of course we will help you as good as possible
In general the flow rate does not influence the cooling performance very much. Even if there are many rumors physics says that the advantage you can achieve is very small.
An example: The maximum temperature difference in one single circuit is about 1°K. So this is the theoretical maximum advantage wich you can achieve when having a higher flow rate.
So the pumps you choosed are absolutely right and more than enough. Unfortunately i do not know the water blocks you mentioned. When using innovatek blocks i can say that one single circuit would be ok.
2)
3/8" is more than enough. Size does not matter in this case
3) No..the pumps you choosed are absolutely ok ! Absolutely silent and powerfull
I hope we could help you !
Markus