Quick thoughts:
1) Echophon is no longer in production, so you'll probably want to look for a Mimeophon instead
2) Surface has a lot of detractors, so I'd suggest looking at Plaits as a comparison which folks claim can do really good dub chords
3) PNW + Batumi + Octosource might be overkill in a rack this size, especially without some attenuators
4) So, yes you could use some attenuators/offsets, as well as logic modules, utilities, etc. Your rack would be considerably spiced up if you dropped in some Ladik modules, c.f. 4 step sequencers, sub octave processor, comparators, any of his LFOs, transposers or something like a Cold Mac
5) A Links and a Kinks would do a lot of work here (as they generally do)
6) You could use some sub-mixers for CV and audio both (Links would help but you'll want more)
7) You have a lot of larger modules here, which is ok to an extent, but if I were you I'd look at removing one or two of them (probably Voltage Block but I'm not an expert on it)
My 2 cents
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