I looked at the Arturia RackBrute 6U with almost 3x the space. (You can find a rack sketch in my profile.)

I cannot truly express how much I dislike the rackbrutes... I could write whole sentences about it, the main point being the rack wart... why waste 5hp for a power input module??? really the tiptop mantis is a much better case (bigger/better power/no rack wart) for about the same money... get a mantis... or don't...

your linked rack is private, so unviewable

This might me the perfect size for me actually because it can (for now) fit my Neutron as well. The Neutron supports Eurorack rails and would be a great utility kit for the other modules: 2 VCOs, LFO, VCF, two ENVs, S&H, and even a delay! I can already see that this makes so much sense if I can interface those with my new modules.

of those, only the s&h is a utility as far as I'm concerned...

I'd want vcas as well... at least a quad...

Good point, but let's compromise on 2 VCAs + 2 LPGs ;-)

LPGs are intended for audio, think of the poor modulation... vcas are useful for cv as well as audio... if you are going to skimpon this I'd suggest one of the 2 channel veils clones - so you can get a second one in the future and correct your folly... the ability to cascade is important as it means you also get vc mixing...

hmm... I suggest some time spent thinking about the contents of my signature...

So you're telling me I need more controls/utilities? I added a bunch in my new rack, and then I'd now also have the Neutron. That ought to be enough for my first steps.

no, what I'm telling you to do is think very hard about the architecture of synthesizers and what makes modular actually make sense...

for example - if you have just an lfo, an envelope generator, a vco, a vcf and a vca - you have a very very basic monosynth... if you add in some utilities... let's say a simple mixer and a mult and some attenuverters you can mix the waveforms of the vco to create more complex ones before filtering the vco and you can modulate by different amounts the various parameters of the vco, the vcf, and possibly the envelope generator - giving you a much more interesting monosynth for very little extra cash - utilities massively increase the patching potential

can't see them (see above)

won't you be using the neutron as a voice so tying up the components? and see above

I take it you have an external mixer for end of chain mixing?

how are you going to raise the levels of the external synths to modular level fir processing?

Yes I run my other synths into an external mixer to get a line out/headphone signal. Eurorack output would plug into that as well. But like you said, I'd want a mixer in my rack for some down mix/level adjustment for sure.

almost definitely more than 1 mixer (which is why quad cascading vca - ie vc mixer) and some amplification (full size veils clone as it has lots of gain - enough to raise line level to modular level - as well as being a quad cascading vca)

"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