If it is working, then your proved that it works !
you should be able to get a second device that uses the same voltage and that way to share one power supply.
the options are many.
get a larger single CPU and replace the feather and do it all with one. ESP32 ?
get a smaller board that uses the same voltage as your feather, use one power supply, but split
I have a WEMOS-D1 with a SD card shield in my stock... not used yet.
the D1 does not have a lot of pins, only 1 analog pin.
but the fact it can have the shield added makes it very convenient.
I skimmed your code, lots of repetition, not a lot of memory for the code. I ASSUME the bulk is the libraries.
I wanted to compile your code with just libraries and then again with just the code to see the memory use for each part... alas, mid-week is not my free time.
if all you need at this moment is a working prototype, you seem to have it.
since you got an Arduino to work, you can get it to work in any of the other forms. UNO/NANO/MINI....
if you need a 100% completed project... you waited to the last minute. you must be a student or an American....