Mat, this build seems pretty solid to me.
The 3 points I have questions about:
-- what will PNW be doing in this setup? It's a great module, but I don't see obvious uses for it here
-- why Scan & Pan vs alternatives or other uses of that HP?
-- why the DUSG? Wogglebug + ER101 + Quadrax + QX already give you a lot of CV for this size a rig, I'm not sure DUSG adds a lot of value alongside your other CV, and it sure takes a lot of HP. If this was my setup, I'd be tempted to put Joranalog Morph 4 where DUSG is. Morph4 is totally different than DUSG, but you could do interesting things in this setup with Morph 4 such as pull several outs from DPO and morph them (at LFO, sequenced or audio rate!) or use it to morph CV that's fed to something else.
Those are good questions and thanks for asking them. I can't promise to give definitive (or even coherent) answers but my thinking was as follows...
PNW is in there to supply a clock to the ER101, which as I understand it, doesn't have an internal clock. I could get a clock from the Wogglebug or the Quadrax or the DUSG but I won't be certain of the BPM with any of these, and I thought that might be useful if I wan't to take anything into my DAW. I also imagine myself using it as an LFO and an additional source of random. But, it might be overkill, as you suggest.
Scan and Pan - that's there I suppose, because I'm trying to recreate the Buchla Skylab, which has a similar mixer (6 channel I think), with the ability to pan the inputs into a stereo field. It looks like it would be kind of fun to create stereo movement. I think Sputnik do one that is even more similar to the Buchla and other smaller options are available but I haven't researched them. Verbos is a pretty reputable brand I guess, and I see the Scan and Pan as the final point in the audio chain.
DUSG - you might well be right about this. I have asked myself the same question (above in this post if I remember rightly) but I guess there are quite a few other things you can do with it. I have considered swapping it out for Maths, which would give me the advantage of another mixer, attenuation, inverters, more logic possibilities and a smaller hp footprint. I might have to end up doing this because I'm not sure how available the ER101 actually is, so I may need to look at another sequencer - possibly the Rene Mk2, which is bigger.
I have never heard of the Morph4, which looks funzies (as my daughter says). I'll check it out.
And yes, I know what you mean about the TipTop Buchla - I imagine it being as hard to get as Beads - frustrating when you decide on a module and then it is unavailable. First world problems of course and I'm very lucky to have the modules I do have already to play with.
Choices, choices, choices... Sometimes I think I should just get a Buchla Easel or a Make Noise Shared System and be done with it... :) I'm sure I'd have a lot of fun with either.