#2
If it's not effecting your playing then leave it be. If it's annoying you (like it would me) take it to a tech and tell him what the problem is.
#3
If you're not sure then take it to a tech and ask them to take a look at it; you can also ask them to show you how to tell for future reference.
R.I.P. My Signature. Lost to us in the great Signature Massacre of 2014.

Quote by Master Foo
“A man who mistakes secrets for knowledge is like a man who, seeking light, hugs a candle so closely that he smothers it and burns his hand.”


Album.
Legion.
#4
as a victim of a horribly twisted neck, what i can tell you is it won't affect your playing at all.

unless if's very very badly warped during which the action height around the 12th fret area will be raised to a point where it is almost impossible to play.