u/Competitive_Smoke266

I am designing a 4 layer carrier board for raspberry CM4 and not sure of the type of layer stack up to use .My design has a 12V supply stepped down to 5V for the CM4 and a separate 3.3V for my RS-485 channels .These two channels have independent and separate grounds attaining galvanic isolation.The signals on my carrier board includes I2C SPI UART and the high speed Rs-485 signals and other booting signals .Which stack up should i use and how do i handle the different grounds within the stack up ?How do i reduce EMI and ensure reliable power for my board??