"at what bank angle the spoilers start to crack open?"
At 8 to 14 degrees control wheel movement, the spoilers will begin to crack open (according to my 744 engineering training notes)
"what minimum distance do you need measured from the a/c nose forward to a possible obstacle to turn 180 degrees on the spot?"
At the moment, the only value I have available is for the distance from the cockpit, forward, with Body Gear Steering disabled, of 59 feet.
Hope this helps.
Regards.
Q.