#2
maybe the person tabbed it for a single guitar?? Usually when there are two guitars, the tab will have guitarists' names, or something like "guitar 1; guitar 2" to indicate parts.
#3
By knowing what happens in the song.. if it's the basic rhythm then obviously it's the rhythm part.. if it's some fancy stuff over that.. then that's the lead.
As for the other parts.. what's the big point of labeling it? If you're a rhythm guitarist and a part isn't considered to be played by the rhythm guitarist in the song, it doesn't mean you can't play it.. Just pick either part and play..
#4
yeah, i agree. It looks like it was intended for one guitar.

the very first part in that tab is the rythem and is played a bunch of times and continues under the intro solo, normally.
theres really only two or three main rythem parts that just repeat over and over and its really just a variation of that first part. the rest is pretty much lead. Look at other tabs for this song and it should break it down better.