I use stairs for training = up and down, for hours. Put on some good music, fill up your backpack with waterbottles, and have fun. I also just find a hill in my neighborhood and go up and down for a while.
Good point about rodents. We use a crittersack and try to hang our food from a tree or a hiking pole stuck in the rocks. We usually leave the rainfly, but bring a full tent because I don't like the creepy crawlies - and do shake out the scorpions out of your boots in the morning!
re: hiking boots. On the main corridor trails, you could get away with light hikers or even good trail running shoes, although I like something with ankle support. The secondary trails get a little trickier, but even those could use lightweight shoes. One thing I've noticed that should be checked ahead of time - I've discovered that my favorite shoes are 7-mile shoes. With a weighted pack, they're fine on short hikes, but after 7 miles or so, I can feel every pebble. So, check your equipment.
For 3 days, I get to part of a thousand other journeys.