Sorry for missing this; J9 is the power supply if you would like to supply it through the J1-8 headers. It's separate from the 3v3 supply.
Here is the correct wiring (a bit messy)
Yes. The SPI data/clock/#DC can be shared between a few OLEDs (e.g. ELO or SCS-OLED) with a separate CS to each display.
Or you can power the displays directly from your PSU. Depends on the current etc.
I think I did it this way as Core J10B is wired to 3v3 (3v0 on a Disco board). Generally the logic levels shouldn't be mixed. It's just a matter of how the display expects its data.
Just follow the normal LCD setup by defining the desired number of displays through the bootloader app. I think the first 8 are still selected by J15, but I'm sure you could configure 64 lines using the Disp Driver CS if wanted.
It may be useful to power the driver at +5V if the OLEDs are locally regulated.
Sorry for the lack of updates in the meantime. The last pieces of the puzzle are being worked on. Adrian has a tentative completion date of the end of April for case prototypes, so after testing these we will endeavour to keep our Spring target. :)