Your scenario is very doable.
The fans may be controlled from either the D5 NEXT pumps or the aquaero, whichever is most convenient for cable management.
I would not use the aquabus connection between the pumps and the aquaero, keep them all on USB.
This may require you use a
HUBBY7 internal USB 2.0 Hub if your motherboard has insufficient internal USB 2.0 ports.
The Δt between the loop temperature and ambient temperature, to control your fans, can be set up on the aquaero as a virtual temperature with the aquasuite, one for each loop.
With the USB connections, and the aquasuite windows service active, you will be able to see all values on all 3 items in the aquasuite, giving you full control capability.
The only other option I would suggest is a
Flow sensor high flow G1/4 in each loop. I have not used the D5 NEXT pumps, but I have seen several posts regarding the virtual flow sensor's limitations and complexity with calibration. If you do get the High Flow sensors, don't forget the
required cable which is not included.
For planning purposes, the aquaero has 4 PWM fan ports and 2 flow sensor ports in default configuration. The D5 NEXT pump has one port that can serve as either a PWM fan port, OR a flow sensor port.
I am not clear on your heatkiller question, maybe someone else who is will help.