I would like to wire a 100 amp pool sub-panel 250 feet away from my main 200 amp panel, and I need to provide 220 volts to some equipment. I have a few specific questions:

1. How do I determine whether the main panel has the capacity for a 100 amp sub-panel? Note that I have two separate 200 amp main panels. It's a big house.

2. How do I determine whether to use aluminum or copper wire? What are the pros and cons besides price?

3. How do I determine what gauge wire to use?

4. How do I calculate voltage drop, and what is an acceptable drop rate?

5. I'm planning to move the panel in about a year, but in the mean time, the panel will be only about 200 feet away. My plan is to use one 250 foot line and coil the additional 50 feet of wire next to the main panel until I'm ready to use it, and then just pull it through the conduit when I move the sub-panel further away. That way I won't have to splice the wire when I move the panel. Any safety or other issues with this?

Thank you!