#1
I just loosened my strings because i had to stick my hand in there to re attach the strap button

when i was winding them back up i thought i was winding the b but it was actually the high e and i over tightened it and it broke

ive got a 12 from an electric set but not an acoustic, are they the same? I'm probably going to use it anyway because the stores are closed, but im just wondering
#2
They're both plain steel, although electric strings normally have some kind of plating, but it shouldn't matter too much. Also, a 12 in electrics is generally lighter than a 12 in acoustics.
#3
really electric 12's are lighter? isn't that a measurement though?
#5
The unwound strings are pretty much made of the industry-standard "music wire" in standard gauges.