1 - probably around 30lbs, and almost certainly hi-ten steel, not chromoly.
2 - no, it's a coaster brake and there is no such thing as a fixed gear coaster brake hub.
3 - answered by seller.
4 - it's impossible to tell from the photos if it's drilled for brakes, but there are eyelets on the rear drops for a fender and rack.
You'd have to replace the rear wheel if you want a freewheel or a flipflop hub (but I don't know why you'd want one if you "don't want to be pedaling all the time.")
It doesn't look like a great deal to me, I don't think it's much different from a cheap cruiser that you could buy new from a department store for about the same money. You can certainly do better if you're patient.
I wouldn't suggest posing these questions to the SS/FG crowd...