Advices on adding 1 rack to my system

Further to what pol has mentioned (I also couldn't see the pics) it is also good to bring the external synths into the Ae for further colouring.
Agree the Slew and MM divider are key along with Beat divider and Logic. Trip too for extra randomisation. For the Sequencer I would receomend the seq8 *2 over the Seq16 as there is a random mode.

In that case of bringing synths into Ae, I would recommend some filters, Kuzmin is my preferred at the moment, also SignalAmp or Boost to enhance the signal in the Ae, 2Env's to bring the Outside voice in time with Ae (Can sometimes help no sync available for outside synths or samples)
Mixers are also good for this MM33 or Moco or 4attmix/fader/Dronx are all good.


  

EDIT : now with the good picture of the 20u after your advices


Thanks for your answers which are very useful and questionning....

here are the screen captures of my actual rack ( 16 u) and my 20u proposition rack.







I also have to say : I was trying to avoid a 4 IN/OUT module or audio mixing/ fx module as i can use HP AMP for audio output,and the 4 IN/OUT from the master, and I also have a Dupont cable /  1/8 jack PCB 32 points matrix that would re-route and multiple a lot of audio signal and/or cv / gate ( of course have to take care of the 0-5V limitations).

2 signal amp or more vca is always a point to add, ( I thought 6 VCA within the 2 rack system would be enough, but... I'm a noob on using VCA and the rest) ..
I would prefer 16 sequencer to get longer sequences ( and using sequencer is for me a way to introduce order when 2S/H and MODULATORS coupled can help for randomizing .... )but it is definitely interessant to look at 8sSEQ + TRIP model .

(EDIT : SEQ 8 seems to make it with the CV RAW outputs that look great !)

I feel like missing something obvious, so i wll reread the AE Modules wiki

Thanks again for your opinions.