I did some quite similar recently, built an accurate ACV/DCV voltage source...
D/A was 20-bit AD5791, controlled via SPI @15MHz by a dsPIC33 @128MHz
Might be some inspiration!
https://www.eevblog.com/forum/metrology/diy-acvdcv-calibrator-with-ad5791/I used a 4-layer board, stackup:
Top: Signals and available space Ground planes (Digital and Analog)
Inner1: +15V
Inner2: -15V
Bottom: Ground planes (Digital and Analog)
The only connection between Digital and Analog ground is made on Bottom side of PCB, under the D/A converter. I opened up a rectangular area in the solder mask to be able to solder a wire between the two ground planes.
Used lots of filtering with ferrites and decoupling on the supples, isolated SPI interface and dedicated ground planes.
Important is to not place components or traces in "wrong" place, digital and analog traces and components must not be placed in same zone (on any layer). Good luck with your project!
