By the time I get to work tomorrow, I’ll have done 1000km this year
Asking for advice related to riding a bike so often that you start wearing parts out within a couple of months is not.
Less than 100 miles a week? That’s not really big mileage is it? I’m sure there are a lot of people on here doing more.
Doing it with shoes (or a single bike) is easy, it’s one variable. Where you are complicating it is wanting to note 50 variables, it would be a daft programme that could keep track of it all.
I don’t see why you don’t just make notes in any of the tracking programmes (or do it in Excel), just note “new BB” next to a certain ride, colour code it if you want, then when you replace go back and check mileage.
Don’t get it at all, there’s too many variables IMO, but maybe I just don’t ride enough to benefit from it!