yup fastfret is basically oil/lubricant that makes your string slippery
and ALSO protects it from rust

little info, if you play your guitar everyday like I do,
the natural oil from your fingers will prevent rusting... to a degree

Hmm maybe,
but there was one time where I didnt play for a few days just to find my strings rust - and that was a brand new set of strings
I think it's more of a factor of humidity - like most things outside would naturally rust
Not sure, I don't wipe my strings... except when cleaning the dirt