1. What temperature do you suggest I use to cook them? 
• 400°F (potatoes are done when internal temp reaches 210°F).
2. Will it help cooking times to use both ovens - 3 racks?  Spacing of potatoes?
• Yes, use both ovens.  Poke the potatoes a few times and then place them directly on the rack.
3. What should I expect as far as cooking time?
• 1 hour for the larger sizes, I would plan on 1 hour 15 minutes max.
4. We will be in the mountains. Will the higher altitude affect the cooking time?
• The altitude should not affect the baking time of potatoes.

Here are some additional links that may be helpful in baking a large amount of potatoes at once:

• Baking Potatoes for a Large Group (150-200 people)
• Baking Potatoes for a Large Group (80 people)