Can be done, but the question is how you want to control everything in the end.

At first: the D5 PWM pumps from EK will be a problem since they are not conform with Intels PWM specifications. They are missing an integrated pull-up circuit for the PWM signal. It is possible to add this with a little modification. Without this mod you could only voltage control the pump which will come down to a very limited range. When voltage controlled you can connect only one pump per fan channel. If PWM controlled you could put both to one channel and get the power directly from the PSU (recommend).

I assume the DDC pump is a regular one that can be only controlled by its voltage.

In theory one fan channel provides enough power for all fans if you want to control all of them the same way. The problem is I can not tell if 10 to 12 fans might alter the PWM signal in a way that they can not be controlled anymore or only in a limited range. To be on the safe side you should split them into at least two groups.

The temperature sensors are no problem.

I do not know the mentioned flow sensors in detail. If they work with a open collector signal, 5V supply voltage and at least 100 impulses per liter you can use two of them with the aquaero. One sensor on its dedicated header while the second one can be connected to fan header #1. Its configuration can be switched to act as a second flow sensor header but this also means you can not use it for anything else.

So in the end you will need at least one poweradjust 3 controller to add a third flow sensor header. This will you would have four fan channels - if that is enough depends on how you connect everything or how you want to control it.

FWIW, the EK DDC pumps can be controlled just fine. I run their dual top DDC with no issues including being powered by the A6 as well.