Avocado tree: pruning advice

[ApidAdi]

My aunt gave me an avocado tree that's probably two years old, and it's never been pruned. It's about 6 feet tall, and leggy; it only has three skinny branches. I've read that you're supposed to prune back half the plant's height (leaving a leafless stick) once it reaches 8 inches tall to encourage/force branching and a shorter, rounder habit. I know the reason you can do this when the plant is young is because it's still feeding off the cotyledons. Will the roots have enough energy for me to try that method with my sapling or should I just trim the branches back as is?

Also, I kind of want to plant it in the ground. Anybody know if it does okay in zone 8b?