Three things I wanted to address about my rack:
1) VCAs. The more the merrier right? My DIY Dual VCA is doing well, but I often find myself needing more control, both over audio signals and CV. Modules that I've been considering for this are Intellijel Quad VCA and Mutable Instruments Blinds.
Veils over Intellijel quad - veils has more gain (upto +20dB) and sliders + as @Lugia mentioned it;s smaller - which is sometimes a good thing - in this case it is
Blinds is bi-polar - which is useful - but makes it difficult to 0 - so if you want silence from your vcas then not so good
2) Random CV modulation. This is a big one for me. I've been on a quest to create quasi-random CV and LFOs for my ambient generative patches. I've been able to get away with it a bit using Tides and some CV mixing. I love randomly modulating the voices I use! From my research so far, I hear Mutable Instruments Marbles is great for this.
Marbles is like a triple TM with extras - really useful - also has gates and a fully random channel - I really like mine - used in every patch - might want to dump the tm and tune (I've got them too - and these would be the first 2 modules to sell if I decided I needed to)
3) Voices. To me, it seems that I don't have enough voices in this rack. I mostly find myself using Pluck, uPlaits and Rings, but is there another voice that sounds great ambient-wise, especially when passed through Clouds?
in this size case I think 3 voices is more than enough - as there is not enough space left over for the important things in modular
I try to think (very loosely):
sound sources < sound modifiers < modulation sources < utilities
as this way you can get more variety for your money and hp
a single sound source can be processed by multiple sound modifiers etc NB a sound source can be multiple vcos etc hence loosely
things I would think about:
you probably need a bigger case (or maybe just another one) - I use 8 cases the smallest of which is 6u/72hp - most of which are diy - I really like the befaco excalibus for power - it's very quiet and doesn't take up racks space (and there's a diy kit version - which is easy but tedious)
fx aid xl - a great little multi-fx module - loads of algorithms for you to choose from - I particularly like the lofi one (stereo zvex lofi junkie) and a lot of reverbs and delays - I'd probably get a couple
long envelopes: xaoc zadar can do some seriously long and complex envelopes
mixing - you look like you need a stereo mixer (rings, plaits and clouds are all stereo (or dual mono) modules - some stereo spread may be good
a filter might be a good diea!
"some of the best base-level info to remember can be found in Jim's sigfile" @Lugia
Utility modules are the dull polish that makes the shiny modules actually shine!!!
sound sources < sound modifiers < modulation sources < utilities