Starting with a minimally-sized rack isn't useful. Trust me. It's always better to have room to grow into, because what will invariably happen is that you'll realize something about your first build that could be improved on by the addition of a few other modules. But without open space for those to fit into...well, you'd be kinda stuck. If you come up with a build that fits into, say, one row of 104 hp, then have two rows of that space, because you'll find all sorts of ways to expand that first 104 hp row's capabilities and without a way to act on those ideas, you'll be shortchanging yourself creatively. Versteh?
And here, we're going to run headlong into that limitation...
OK, if the idea here is to work along West Coast lines, you need to keep in mind that that method entails crossmodulating things at audio frequencies to get very complex spectra. Don Buchla's methods involved taking really simple oscillators and providing a number of different ways that they could modulate each other. Have a look at some obviously West Coast oscillators, for example: the MakeNoise DPO, Sputnik's Dual Oscillator, Radical Frequencies' Dual Precision Oscillator, or Verbos' Complex Oscillator. In all cases, the module contains both the oscillators and a lot of options to crossmodulate these under differing types of control. While the Cloud Terrarium is an awesome oscillator, it's not exactly set up like that; that module is more of a wavetable-scanning type of oscillator, which is cool in of itself (just ask Wolfgang Palm and the folks at Waldorf) but not exactly suited to 'pure' West Coast. You could include it alongside that sort of synth architecture as an incoming source, but as the sole source in this sort of synth, it's not exactly right.
Next up, West Coast derives a lot of its sound from the use of low-pass gates to shape the final amplitude and timbre. These are circuits that combine a low-pass filter and a VCA under the same modulation control signal. The idea behind these was to create a circuit that behaved how an acoustic source did when a sound decays: higher partials fall out faster than lower, and by the use of a vactrol, the decay gets shaped in a similar way as a resonating object in which vibrations decay over time. In theory. But in actuality, there's loads of ways to make totally unnatural sounds with LPGs, especially more recent ones that offer some controls that Don Buchla didn't either consider or have access to back in his day.
Maths definitely fits the West Coast scheme as a modulation source. It's actually a derivation of a Serge module, the Dual Universal Slope Generator; the Serge was a follow-on to Buchla's 100 and 200 series ideas, with a lot of rethinking of how signal flow should work and a stronger reliance on filtering for spectral shaping than in Don's earlier systems. In a way, the Buchla is the 'San Francisco' synth and the Serge is the 'Los Angeles' synth: similar, but definitely different. The Batumi, though...that's more akin to a typical LFO, albeit in a four-pack module. To get closer to a West Coast method for envelopes and modulators, you'll want a bunch of AD, AR, or ASR-type envelopes in which you can vary the 'rise' and 'fall' times, plus have a lot of triggering and cycling options. By combining these with the low-pass gates I mentioned above, then you get right into that West Coast 'pocket', sound-wise.
As for the Erbe-verb...the key to a lot of the early Buchla sounds, especially in the 100 series, was reverb. Back then, Don used a spring, because that's what fit into the space of the 100 cabs of the day. The Erbe-verb is actually an extremely complex digital device, but not at all out of line for the sound in a modern-day context. It allows the modulation schemes found in West Coast methods to also affect the reverb parameters to the same sort of complexity as other devices in a typical West Coast signal chain.
The Morphagene, though...that's a whole different thing. With that and the Phonogene, Tony Rolando is offering a modular take on concrete-type sound manipulation, either of sounds in the synth or ones coming in from outside. It's neither East nor West, but more like Paris, where Pierre Schaeffer first envisioned his Phonogene device for altering sounds as they travelled along a tape loop, to allow a more 'playable' aspect to tape methods, which are normally anything BUT playable. As for the Morphagene, it combines ideas from that plus granular methods from digital source manipulation, so it's a bit less Schaeffer and more Francois Bayle or Jean-Claude Risset in that aspect. It's not really West Coast, therefore, but it fits really well into the experimentally-oriented sound of the West Coast methods.
So...how to proceed? I suggest taking a bit of a stop to study the different modules on MG, but also having a look at Buchla's present-day website (https://buchla.com) as well as the outside-maintained site for Serge (http://serge-fans.com) so you can get a better handle on the contexts behind the whole West Coast thing. Eventually, you'll see the connection between the 'originals' and the Eurorack derivations of those, and that should result in a better-informed position from where to start.
Then start with a bigger case.