I'm going to be out of the country here for a while, and by the time I get back, it's not gonna be P-Car weather. Is it better to get the oil changed before I store the car, or after I get it out again in the spring?

 

Before. Oil that has some miles on it can contain water and unburned fuel, depending on how the car was driven before you shut it down. Fresh oil for storage.

 

I always change mine before winter storage. Then I put on a battery maintainer and drive it up on Tire Cradles. http://www.tirecradle.com
Some people use multible lavers of carpet with good results.
These tires will flatspot if left in the same place for a long time. High air pressure will just make the spot harder and smaller. Jacking the tires off the ground is not good for suspension parts. I have been doing this since 99 with perfect results. I never start the car again after I put it up for the winter.