Custom board, uC and ADC recommendations

I have a project I'm about to start, and wanted to get some recommendations. My requirements aren't particularly complicated, but I thought that aside from my general google searches, I'd ask here.

I'm designing a custom board, and I want to use a microcontroller that's compatible with the Arduino IDE. I need to have either on-chip or as a cheap external peripheral a minimum of (3) 24-bit delta-signma ADC channels. I also am going to be using an EPD (e-paper) display, which will likely be SPI or I2C connected but I don't want a pre-built module. I have a display supplier that I regularly use, but I know they aren't going to provide a pre-made arduino library. I've seen some EPDs that have arduino libraries, but those display modules are a lot more expensive than what I'll be using (I guess that's one trade off).

For the micro, I'd like to go 16 bit with 16 or 32k of RAM, speed doesn't matter, but it does need to have a low-power (or ultra-low-power) mode that draws microamps when in standby (i'll be powering from 2 series 3V lithium coin cell batteries, and at the duty cycle I plan to operate, I shouldn't use more than a few hundred milliamp-hours per year).

Any recommendations?

Build the project on a breadboard first.

...R

For the micro, I’d like to go 16 bit with 16 or 32k of RAM

Plenty of 8 bit AVR’s and 32 bit ARM’s. 16 bit? Zip. Nada. Zilch.

If speed doesn’t matter, then 16 bit doesn’t matter. An 8 bit AVR is a pretty capable architecture and the pico power variants run just fine with 3 volt coin cells at 8 MHz.

Add SPI SRAM/FRAM and ADC parts. Will likely need a good reference voltage for the ADCs as well.

Small RAM and displays are not the best combination.

For your ADC, if you really want 24-bit resolution you're going to have to work really hard on very stable references and interference free connections to your sensors. Each 1-bit step is 0.18 uV on a 3V scale, small enough that even junctions may start to matter (the different metals touching act as thermocouple).

To my feeling the 24-bit ADC requirement is very much at odds with the other requirements (especially the low power, battery operated part).