In Europe, short distances are in meters, longer distances are usually in nautical miles although kilometers can be seen every once in a while as well. Statute miles are about the only thing not used.
Altitudes are given in feet in most of the world, except for China, Russia and a few other places where they use meters. Military aviation and gliders used meters in my part of the world (N. Europe) until quite recently when the military started using both systems.
Speeds are generally in knots, with some places using km/h AFAIK. And again, the same situation regarding the military and gliders around here.
Vertical speeds are either in feet per minute or meters per second.
Weights are pounds mass or kgs. Fuel is measured by weight or by volume. In the latter case, I've seen litres, US. gallons and imperial gallons.
Regarding altitudes, all altitudes are measured by pressure altitude as compared to a reference pressure. At lower altitudes, this reference pressure is what the pressure would be at sea level, hence giving a correct altitude above sea level. At higher altitudes, where you care more about using the same reference as all others to stay clear of traffic rather than using a true altitude above sea level, you switch to using a standard sea level pressure as your reference pressure. When flying on this reference pressure you do not talk about feets of altitude at all, but rather about flight levels, which are in hundreds of feet. I e 21,000 feet read on the altimeter on a standard altimeter (reference pressure) setting would be FL210. Your Mont Blanc example may or may not be into the flight levels. Of course gliders and military aviation tend to care more about their altitude above the place where they land and take off, using the Mk. I eyeball for traffic and terrain avoidance, so they often use a reference pressure setting giving an altitude of 0 feet when landing on the runway.
If you state location, aircraft type and country of origin of the intended outfit I think we'll be able to have a long, interesting and possibly informative argument about the units to use in here.
Confusing? Yes, indeed. In a former job, I used kg-inches, pound-meters and pound-millimetres a lot. Go figure.
I'd state with confidence that we are at least not using fathoms per forthnight for anything, unless I was certain that someone would pop up and tell me that company so-and-so in some remote corner in fact have their altimeters calibrated according to this standard...
I thought I was doing good trying to avoid those airport hotels... and look at me now.