1. You shouldn't worry, you're training and will be ready.
2. The advice about getting up to elevation (6-8,000') and hanging out there to acclimate before your climb is good advice --but we don't always have the time to do that. What can hurt you is going from sea level to 10k all in one day.
3. Drink lots of water. Pee should run clear to pale yellow. Pay attention to this one!
4. Again, don't worry, you're going to have a great adventure.