yes

Yes, but keep in mind that burrowing rodents, like gophers, can chew through the tubing seeking water, and with it being underground, it is harder to locate the leak. Alternatively, you can use regular PVC irrigation pipe for the the underground portion (Dig has adapters for this, they sell them at Home Depot).

You would want a tree to be self-sufficient in a year or two. It is a lot easier to drag a hose a few times than put in an irrigation system.