I can't help you with much of the question but I'll tell you what I've heard about watering new trees. When I bought some trees a few years ago the guy who sold them to me (and planted them) told me to water them once a week with five gallons per inch of tree diameter. He said that the best way to water them was to take a five gallon bucket and drill a 3/16" hole in the side close to the bottom. Set the bucket next to the tree and fill it with water and let the water empty slowly into the ground. (He said that if you try to water with a hose it comes out too fast and most runs off.) Anyhow, he said to do this for the first two years and he'd guarantee that the trees would survive. Six years later and all except one are thriving--that one the deer browsed so badly it didn't make it. He said that after the first two years of deep watering they'd have deep enough roots to survive even the worse dry spells we have around here. YMMV!

That sounds like a good idea for new tree plantings.

My thing with putting the a soak at the base of the tree is that the runoff goes 360 degrees all around the tree and covers most of the water inside of the drip line.

Now that most of my trees and shrubs are 2 years old, I'm think I should start watering right at the dripline, maybe just outside of it.