#1
Does it have any effect on sustain?
And a wise man once said:

"7 Strings are more brutal than 6"
#2
everything has effect on sustain
and this would probably effect it a decent amount
The nice part about being a pessimist is that you are constantly being either proven right or pleasantly surprised
-George Will

Also caught her playing fallout boy on my guitar, changed my strings and cleaned it the next day.
#3
yup..it has a huge effect...it can go as far as killing the sustain completely