Well - I do think that things like measurements matter, and be it only for the sake of consistency and the understanding of the readers.
I suggest metric and universal for industrialized/technological areas - however 'tribals' would in my opinion tend to use 'thumb', 'handspan', 'pace', 'man-heighth' and the like.
On currency I favor a multitude - and not all must be based on metal (!).
Let's keep it decimal, though.
Remember the setting is the early 1900s - at that time
- literacy was high (in technologically developped areas), but far from 100%;
- agriculture was spread much more than industry. Though the big fortunes were made in the latter, the majority of the people were poor;
- not everybody had a watch, timekeeping was not by seconds or minutes;
- ...
As HandEFood said, there is ways around a lot of those traps - but watch out for them.
Note:
Lews mentioned airplanes - are we, do we want to be, at that stage yet?
