In his video he listed the modules he was using to get his sound: Qu-Bit's Bloom, Mutable's Peaks, Mutable's Rings clone, and Qu-Bit's Prism. ... So if any of you modular veterans have suggestions for modules that can produce similar effects as the afforementioned ones for a better price, I'm all ears.
Ok, I'm writing this from the perspective of trying to save you money instead of "hey look at this cool thing that will totally save your music":
-Qu-Bit Bloom: is just a semi-generative sequencer. Sure it has some fancy "fractal" morphing of sequences but you can get simmilar results using the Microfreak's sequencer and arpeggiator and the Spice and Dice parameters. In addition, your Pams can effectively function as a sequencer for secondary melodies and voices. I would still recommend getting a dedicated sequencer in the rack eventually but hold off on Bloom unless you're sure it's exactly what you need. Ditto on Squarp. I'd say it's too huge and power hungry for a rack this size, you don't have 8 voices to sequence and there are more efficient (smaller and chaper) MIDI to CV modules available if you decide to sequence externally.
-Peaks: can be many things including a drum, but at its core it's a dual envelope/lfo. You already have the Erica EG, the ADSR, the Doepfer DLFO and Pams for modulation. You don't need Peaks. It can do other things but unless you've identified those specific functions as necessary it's superfluous to your system (and even then there are other modules that can probably do drums etc. better than Peaks). That said, you have two ADSR envelopes which are more typically used with keyboards, Function Generators or (loopable) AD and ASR envelopes are more common in Euro and if you find yourself lacking space down the line I'd consider swapping one of those out for a more versatile envelope/modulation source (not gonna name modules because the goal isn't to make you buy more stuff).
-Mutable Rings: Plaits has the Karplus algo which covers one of the three modes of Rings. You microfreak also has both a Karplus and a Modal algorithm. One thing that's missing is using Rings as a resonator for external audio inputs but that's not necessarily what you need. Still, if you decide to go down that route, there are many clones of Rings available out there, but experiment more with the Peaks and Microfreak algos first.
-Prism is an interesting module but at the end of the day it's a filter, delay and bit-crusher rolled into one. You have the filter and delay covered in Wasp and Nostalgia. You might either invest in a smaller bitcrusher or another effect, or maybe trade the Nostalgia (unless you're attached to it) for a Prism. Of all the modules listed that would probably add the most to your system right now.
tl;dr: You don't really need any of the modules you listed.
In your intro you said:
My goal with this whole setup was and still is to create cinematic soundscapes with swelling waveforms, resonation, reverb, and basically create a droning enveloping sound that builds, waxes and wanes.
For that, I would say you need more VCAs (currently just one, though the Plaits has one built in, kinda). Don't think of VCAs just as "thing that makes sound go loud or quier", depending on which ones you use, they can also modulate CV, creating more complex modulations, be patched as crossfaders, waveshapers, automated attenuators for any kind of parameter etc. If you want your sound to move, swell, wax and wane, VCAs are your bread and butter.
The second thing here is reverb. You don't have one in your rack, nor is it on your list of modules above. Reverbs can easily smear and stuff and make it "cinematic" or glue a bunch of sounds together in a droning space.
Resonators you kinda have as your sound sources (Plaits, Microfreak), but you might look into them some more. Not sure about Nostalgia but many delays can also resonate at very fast speeds (which is the essence of the Karplus-Strong synthesis also found in Plaits and MF).
In conclusion, you don't really need more modules at this stage, although you're lacking a reverb (unless you're adding it externally) and more VCAs (and other utilities) would be beneficial to have. Work on your technique, experiment, take notes, study the music you want to make. Jameson Nathan Jones has a lot of composition-oriented videos on his youtube channel and works with modulars, Omri Cohen does modular ambient and also has a ton of visual tutorials, mostly in VCV rack, which is a good way to experiment and learn without necessarily buying more modules.
I'm not exactly an eurorack veteran (I've been at this for about two years) but happy to try and answer any more questions you might have.
Good luck!