OLED life is a concern, the screen will only be on when the key is in run to prolong it as much as possible. I found a test of these screens showing they had over a year of continuous run time in them here:
https://hackaday.com/2019/04/23/a-ye...-oled-burn-in/.
Given how much I use the vehicle I'd estimate it will only be on about 50-100 hours a year.
I did come across that Retromini blog a few times in research, but I guess until now I didn't notice how similar it was. Looking at it now, that code could be improved quite a bit by removing the various doubles and floats replacing them with unsigned longs. I'm going to check out this FreqMeasure library though and see if that may be better at reading VSS than the interrupt.