There's lots of variables that affect how much effort one expends in skiing. Key amongst them is your technique -- that is, how efficiently your technique allows you to ski. Other factors include the snow conditions, terrain, and the intent of the skier.
WC skiers typically only ski a few runs a day. Why? Even though they have far better technique than any of us here, they are putting everything into those few runs. So the physical toll of pulling turns with huge g forces is pretty taxing.
Everyone is at a different stage of life, with different technique, with different levels of conditioning and acclimation to the altitude, with different physical assets and deficiencies (such as chronic issues due to injury). So your mileage will vary.
The best advice I can give is to prepare through conditioning and most importantly listen to your body. You will be over loading it. A key part of conditioning is that the overload is important, but the rest is even more important. The rest is when you gain the improvement in condition that comes from loading the body. So don't forget the rest -- either in your preparation, or during the time you are at WB.
And most importantly, work on your smile -- hopefully it will be in permanent presence during your stay!
BTW, if you want to ski terrain at WB, I can't recommend Extremely Canadian enough. Those guys really rip and really improve one's technique to ski extreme terrain. They also will take you to stuff you otherwise would be unlikely to find...