Because we are writing a story rather than playing a numbers game, I don't think that units of measurement or currency matter that much. People can simply write "He paid for the goods" and "He exchanged enough money to Lira to live comfortly for the next week." If someone (as I can forsee for Lews' character) is involved with cash or vast sums of money, perhaps give a comparison of what it could buy: "We're going to make millions each! Which tropical island do you want?"
For measurement, I'd be inclined to say metric (the international standard), but, for the comfort of the writers, as long as they state the units miles or k's (kilometres), pounds or kilograms, Fahrenheit or Centigrade, etc. that should be sufficient.
What do you think?
