#2
I've always called it "guitar drumming." I've never heard it called anything else. If you search that, you'll find some lessons for it!
#3
"Percussive guitar" Very popular now, some artists get very involved with the technique. As in, Tommy Emmanuel.
Actually very old... You can see the roots of this in Flamenco with the "golpe" or finger-taps, and in various "world" musicians.
Bob Brozman, the late slide-guitar master, says that cultures all over the world see using percussive effects on the guitar as just normal playing.