Hey luinnar,
— Buy a Plaits before they are all gone and upgrade it to the latest firmware. You'll hear so many sweet spots in the Orange mode you'll be fine delaying the Cs-L until you have a bigger case (and you can still practice using it for free in your VCV rack anyways). And Plaits offers some noise, drum sources, to cover your concern.
— For ambient, look into Zadar. It is 4 envelopes in 10HP. But instead of ADSR it is 260 different shapes that can be warped, sized, shifted, and reshaped. The length of the shape can go from a tiny fraction of a second up to 30 minutes. And the shapes can be set to repeat infinitely so it's also 4 LFOs. What's really cool about it is that you can use one shape to modulate another. So you can set the first envelope to be warped by the second, being warped by the third and by the fourth. You can make really interesting unique shapes quickly; it's impossible to exhaust and you can save presets if you hit on some good ones. Perfect for ambient stretches that always evolve. https://www.modulargrid.net/e/xaoc-devices-zadar
— Try out the free ALM Tangle Quartet in VCV. It's 8HP and much less cramped than the Doepfer. Intellijel Quad is 12HP so it won't fit your constraints, you'll need to rearrange your rack.
— One recommendation I'd make is to buy Befaco Knurlies. They are little screws you can turn with your fingers. No rack rash. And you can swap modules so quickly and painlessly—I have a big fixed case but also a small portable 64HP, and for Christmas I boxed up some modules and I must have switched things five or six times in an hour playing for my family. I couldn't imagine using a screwdriver.
— I love multis because you can send one cv source to multiple destinations--like a macro control and to keep your modulations tight and musical. Also try the Instruo [1]f in VCV. It is a crossfader, but also attenuates / polarizes a single source, and can offset.
Remember in modular, you can solve every obstacle with a little more space and a little more money. :)
15-20 cables is a good start, but you may find yourself not using more than 10 often. Using your hands to play the knobs is more fun.
That's my advice'ishness.