I'm going to answer my own question number 1.

"Is it appropriate to break partially submerged elbows and apply bends to the portion above ground."

I'm going to go with a resounding yes. Instead of penetrating the ground at 30 degrees (like in the stick model), I'm penetrating it as something closer to 15 degrees, and it's providing more resistance as a result, and therefore higher stresses by some 20%.

Any input on the second 2 questions would be welcome.