Ronin, thanks for the comments. The 531 mixer does seem to also be slightly future proofed with the six channels. People usually talk about expansion in terms of buying a larger case than one considers at first, but maybe this would apply to a mixer, too?
Thanks for the clarification on the Disting and the point about the Springray. The latter was completely not obvious and I would have missed that. Reverb modules feel pretty hard because they are fundamentally pretty simple (we all know what reverb sounds like), but as a newcomer without experience it seems hard to know which criteria to use to evaluate and make a choice.
The 1010 is a good suggestion, but with the 1u MIDI, I will also just be able to wire up to Ableton itself if I need that. And in fact, I plan to do just that early on as I get some experience with the first modules and before I get a modular sequencer.
Also respectfully agree on the active/passive mult. It is not a super big price to pay for future proofing.
If the Xaoc module is the Zadar, that looks really nice, too. Compact and the menuing doesn't look like it taxes the brain too much.
I will take your advice to heart about building in stages and letting the not-full case tell me what it needs.