This accident was really survivable with a 4 points seatbelt....
'Sure looks like it, assuming that the shoulder harnesses were being worn...
to get best glide you keep flaps up as long as you can only when sure of the touch down spot you put them down
Yes, though that older model of the 150 probably has manual flaps, giving the advantage that you can extend full flaps very quickly at the last moment.
It was a compromise forced landing situation at best, and good on the pilot preventing any risk to the public!