Code has to be precise and efficient.
I don't think reading the file to get a single item on each interrupt of the rotary encoder will be fast enough, especially if the encoder is turned quickly.
Can anyone advise what my best approach might be?
Why so little? Surely its not a space issue.
As I don't need to modify the strings or data while my app (sketch) is running, I think my best bet will be to store the data in flash (program) memory instead of SRAM.