I'll start by saying I REALLY don't like the uZeus power supply. It only supplies 500mA to -12V, and your system as specified is already in the danger zone for crapping the supply out (you need to keep the utilization at least under 80%, if not going so far as under 66%, of the rated). Upgrade to a 4ms Row Power 40 which supplies significantly more juice to the -12V rail.
Second, you only need a buffered multiple for primary pitch CV. You can totally use a passive multiple for Gate/Trig, as well as use one for modulation that doesn't need to be dead-on accurate. I'd replace two of your three buffered mults with passive mults and save yourself some money and some power connectors.
As for module selection, it ultimately comes down to how you're going to use the synth. My guesses based on your proposed layout and your statement of "self-standing modular" is that you're looking for something that would be like a "super ARP-2600"...something that has all the bells and whistles associated with a traditional monosynth with the benefits of patching. If this is the case, I'd pop in another Dixie II+ to have three audio-rate oscillators (with the ability to drop two of those oscillators to LFOs) and a Make Noise ModDemix to have a ring modulator (well, two). In addition, I'd substitute the big Pittsburgh Modular mixer for three 2hp MIX modules; one to the right of each oscillator.
I rearranged the system to have a left-to-right, sound sources over modulators flow to it.
You still have 18hp remaining in the bottom row that you could use to add another filter or an effects module or two.