First up, don't get used to the idea of the M32 being in the 7U case. It's a lousy idea. It wastes space that needs to be used for modules which don't have a case, for starters. Then if you factor in the cost of rehousing it in the 7U, given that it already has a case + power, your M32 would then wind up costing you about $765, figuring $599 street for it + about $165-ish for the 60 hp it would occupy in the 7U. Not a good deal.
The rest of the modules are actually quite sensible. The Quad VCA is the correct choice, fyi; the ALM Tangle's VCAs are all linear only. It's necessary to have those, but mainly for CVs and modulation signals where you want that response. Exponential VCAs are the ones needed for audio, because of how our ears respond to apparent loudness (logarithmically). By using the Quad VCA, you can select either linear for your CVs and mod signals, OR exponential to control audio levels...or anything in between due to the variable response controls. Besides, the Tangle costs $10 more.
The DixieII+ is actually a decent choice as well. If you plan to feed the M32 through the 7U's audio path, that VCO will serve very well to double the single Moog VCO to allow for detuning and sync and other things that will be pretty useful to getting a "bigger" sound. In fact, I would suggest controlling the DixieII+ from the M32's pitch CV and then feeding its audio back through the M32's VCF and just presuming that it should be a doubling VCO for the M32. While the Mother 32 does have that Moog LP VCF...it only has the one VCO, which means it only has ONE part of the "Moog sound". Using the DixieII+ along with it fixes that issue to a decent extent.
As far as other VCOs/sources...wavetable VCOs aren't a bad idea as long as you can "scan" the wavetables, PPG-style. That's a big aspect of that sound, and one that comes to mind that has that ability is The Harvestman's Piston Honda, now in rev 3. Another route would be a pair of complex VCOs, something akin to the Make Noise DPO or Sputnik's Dual Oscillator; these are more akin to Don Buchla's 200-series oscillators, in which you have ample internal crossmod possibilities that can create loads of possible timbres before ever getting out of the VCO itself! Very convenient! But don't neglect other exotic possibilities as well, such as multi-op FM VCOs, thru-zero FM-capable ones, phase distortion oscillators (ala the Casio CZ series), etc. LOTS of possible directions there, from simple to utterly insane.
But this is coming along...just take this process slowly! It's not a race; consider ideas carefully, ask for advice/ideas, and the like. And don't expect the first build to be THE ONE...because it won't be. There's always room for improvement, along many fronts.