I think your initial shopping list for the controlling/monitoring related stuff should look something like that:
1x
aquaero 6
8x
inline temperature sensor [1]
1x
high flow sensor[2]
1x
connection cable for high flow sensor
1x
high flow sensor with USB and aquabus[3]
2x
D5 pump with USB and aquabus[4]
5x
splitter for the fans and aquabus devices[5]
1x
4-pin aquabus cable[6]
[1] The aquaero has eight temperatur sensor port but you could connect even a few more because also the aquabus devices have an external temperature sensor port which can be read out from the aquaero via aquabus. I find it a bit questionable to measure the inlet and outlet temperature of the blocks. The difference will be rather small and does not provide much helpful data. Using the temperature sensors on the radiators would make more sense. If the water flows through both with nothing in between, then you should connect one sensor on the inlet of the first radiator and another sensor on the outlet of the second radiator. Together with the flow rate the aquaero can calculate the theoretical thermal dissipation loss. At least this is some useful number. Besides that the general water temperature is more important to control the fans.
[2] This sensor will use the dedicated flow port on the aquaero...
[3]...while this one is basically the same but will be connected via aquabus. It is possible to change the configuration of the first fan channel to serve as a second flow sensor port but in this case you will also use it as a fan channel. I would say that does not make much sense in your setup.
[4] I am not sure if you already have the pumps or not. If not this variant is interesting because it can be controlled through the aquabus interface.
[5] You would use four splitter for the fans (4x 8 fans) while the 5th splitter will be used to connect all aquabus devices to the aquaero. Please note that the flow sensor and D5 pumps with aquabus use the same controller board so they also use the same aquabus ID by default. You will have to connect these devices via USB first to assign unique aquabus ID numbers and for the pumps you also have to change their communication priority from USB to aquabus because otherwise you will not be able to control them through the aquaero.
I do not know your fans so keep in mind the aquaero is doing about 30W per channel. Of course you can only monitor one rpm signal per channel. It is the fan that will be connected to the port marked with "rpm". I am not 100% sure but afaik the ModMyToys splitter forwards all lines which means it will also forward all rpm signals of the connected fans which will not work.
[6] The 4-pin cable allows to use the flow sensor with USB and aquabus to be used without the USB cable (after configuration). Normally the sensor gets its power via USB but with the 4-pin aquabus cable it can be powered through the aquaero so you can remove the USB cable to get everything a bit more organized. Same for the D5 pumps with USB and aquabus but since they must be powered by the PSU anyway, there is no need to use them with a 4-pin cable. A 3-pin cable is supplied with them which is enough to communicate with the aquaero.