#1
I just learned SRV's "Sky is Crying" by ear, so I know I can do it, but it took a good month for me to get everything (working on getting it down now). I'm pretty into that style of music (classic rock, blues rock, that sort of thing). Are there any good songs or anything that I should look at to get me started?
#2
Check Derek Trucks, John Mayer, Joe Bonamassa, The Black Keys, etc. Congrats on learning by ear, it takes a while at first but then it's much more quicker.
#3
Ya going by ear is a very good skill. I'm not sure what songs you will like so I will list a few:

Simple Kind of Man - Lynyrd Skynyrd
House of the Rising Sun - The Animals
Superstition - SRV
#4
I did Led Zeppelin's Living Loving Maid today in about 5 minutes. Or the main riff anyway. That was pretty easy. Also did the main riff to Moby Dick.

I got some good advice the other day. Stick on an 80's radio station and just play everything that comes on. That way, you haven't got time to mess around and get distracted. A lot of the songs follow the same chord progression so after a while, it gets a lot easier.