#1
I've been learning how to do my own guitar setups and have been adjusting my string height recently. I like pretty low action so I was setting up one guitar just to realize that the action near the nut is pretty low while it gets higher. I just used a ruler to see how much higher it would get and I found that the action on the 24th fret was slightly higher than the 12th? I'm not sure if this is normal but if I lower my action more I start to get a bit of a buzz, most notably on the G.
#2
Yes that is normal.
Quote by TheSennaj
And well yes, I'll enjoy the carpal tunnel and tendonitis, because trying to get one is clearly smarter than any word you have spoken thus far.
#4
Your action will usually be about .010" above the first fret at the high E string, tapering to perhaps .063" at the 12th fret, according to StewMac, with .001" relief at the 8th fret. I think that's a bit high (.063" is about 1/16th") -- I've got guitars that have the high E string set to around 1/16th" at the 24th fret, with no buzzing frets. The low E string will generally have a bit more distance from the frets than the high E string (measured to the bottom of the string), perhaps as much as 1/64".

The G string may be running into a fret that's slightly too high at that point, or the nut or bridge saddles may be too low. The nut may need to be recut or the saddle may need to be shimmed slightly. There are sets of understring radius gauges that will compare the radius of the fretboard/frets to the radius described by the strings. You might need to raise the bridge saddle on the G string slightly, or check your frets in that region with a fret rocker.