If you don't live near high mountains for training hikes, then it is likely that you will suffer from altitude sickness with loss of appetite, nausea and headaches. Here are some steps that you can take to minimize the chance of illness.
4. Drink a lot of water during the hike. Do not wait until you are thirsty. You will already be dehydrated. Drink on a schedule. In addition to water, carry powdered Gatorade or another sports drink to add to the water you collect along the trail.
5. Take food that you enjoy eating to help overcome any loss of appetite. Favor carbs over the harder to digest proteins.
To point "zero", what altitude you live at is no predictor for whether you will or won't get AMS. You could live in Denver and get AMS at 8000' or you could live in Los Angeles (as my buddy has for all of his life) and not get any AMS even on the Whitney summit. In fact, they still haven't found any sort of reliable predictor, but they have found that older people tend to get it less, and that's probably because they don't ascend as quickly.
For #4, you can have too much water (mild hyponatremia has been discussed on this site before). Certainly make sure you're getting enough salt while you hydrate. I will start with about a liter or more of water in the early morning for the first several miles on a long day hike while it's still cool, then drink a liter or two of Gatorade, or water with Gu or Skratch in it, while trying to regularly eat food (#5) that is mostly carbs (sugar is absorbed much earlier in your digestive system for energy, and protein requires more water for digestion). Proper hydration actually starts 24-48 hours before, so if you are well hydrated in that period of time, you can save time drinking while on the trail. If your urine is essentially clear, you are over-hydrated.
