for the fans, the splitty behaves like a corsair fan led hub. You have to connect the fans in order, from RGB port 1 to 4, as they will pass data from one to the other.
Since you have banks of 3 fans all the time (3 front, 3 back on each rad) you'll probably want to connect each bank on one splitty. Maybe top - middle - bottom as fan 1, fan 2, fan 3.

with 3 rads in push pull, that's 18 fans. the 1000D can take one or two more on the back, so i don't know what's the 21 ' possibly, you may need another Splitty 4 for the last fans.

With a big case like that, take notes of what is connected to what splitty, on what channel it connects on the FW360 so you dont pull your hair when setting the RGB.

Same deal with the PWM. Here you have 4 PWM channels on the Aquaero i believe. that's a bit short. You'll need one for the pump. for the others, you could connect two splittys to a pwm splitter cable, and drive an entire rad from a single channel. 6 fans on a 30W channel, it should be able to take it, and you could connect all 3 rads on the 3 remaining channels (make sure you set them all to PWM)
If ever you feel you need more channels, you can get a quadro or octo and connect it with aquabus to the Aquaero. It will then behave as an extension with 4, or 8 more PWM channels.

And for the other RGB devices, they just connect straight to the FW360.

For such a busy build i personally would have gone with an Octo rather than Aquaero, or maybe aquaero + quadro, to have more PWM channels. As it is now you'll have to piggyback your back exhaust fans to a radiator channel, so you won't be able to control them separately.

If i were you i'd start connecting the fans and see what i am missing hehe
since you have 2x4 fans on the front that will take a whole splitty 4 for either side
two more splitty for the pull fans on, the other side, two for the top rad etc.. and see as you go what is missing
You could use a free spot on one of the top rad splitty to connect the back fan.

Since you have an aquaero, i'd use aquabus to make a quadro an extension of the aquaero. that's what it's for after all. That will give you an 8 PWM channel Aquaero.
Otherwise if you go for an Octo to connect everything for example, the Aquaero kind of becomes redundant and you may as well just use the Octo standalone (if you don't plan on using features that just the Aquaero has).
It's a matter of preference. You could use aquaero + quadro on aquabus, both units standalone on USB, or same thing with an Octo, or get rid of the Aquaero.. all options would work.

There are many ways to connect and control everything so it's hard to say "here : that's the way to do it, order this and that"