Hi Jim, thank you for your in-depth thoughts!

So, first of all yes, I already own some of those! I own the Plaits, the O&C and the Monsoon. At the moment I have a 84hp 3U cre8audio Nifty Case, but it's almost full and hopefully I'm gonna upgrade it to a nice 104hp 6U Tiptop Mantis case very soon!
So, why the Pico Case? Well... it's mainly for "organisational" reasons with my other gear. I make ambient music and I'm really happy with my Synthstrom Deluge as the core for my system... modular is also nice for ambient sounds, but I find it a bit unplayable in a live situation. I use my modular to sample sounds and then I arrange them with my Deluge, or i prepare cassette loops... but I'm not really able to play it live, too many cables and patching, it's very unpredictable, requires tuning and you never really get the same results.

So, since I still love eurorack and I like to keep things minimal, I decided to make a really small system with a limited range of features I can easily tweak live. I got some really cool results modulating Plaits' harmonic in chord mode and Monsoon's pitch and density with my Marbles, so it's something I already kind of tried... I planned this system with the idea of creating some easy-to-make generative polyphonic ambience while I play my Deluge and the other stuff.

So the modules I was planning to get are the Doepfer LFO and the utilities (which are missing in my bigger case too haha). I thought that having 4 LFOs could be nice to make slow, constant variations on Plaits and Clouds with the off-phase thing. Marbles is a bit too on the "step" side, and it's also bigger. But maybe the Doepfer one is too limited, and I shoud consider something more complex... Batumi maybe?

I totally overlooked the VCA depth!! Haha sorry for this, usually I'm very careful to depth and power specs when I plan my racks XD
So I could remove it and put in something like the ALM Tangle Quartet! Four VCAs in 8hp, it fits perfectly, and I would also get the two additional VCAs.

O&C - yes, I was thinking of installing the Hemispheres for that exact reason! To use it more like a swiss army module than a quantizer on steroids. But - speaking of playability - it could be the wrong choice here (lots of menu diving).
I'll take a look at the 2hp modules you suggested me! Somehow I have to rearrange this.

Thank you so much!