Desirable maximum steering angle Zero means going straight, 90+ degrees is probably impossible. 

So what is the maximum steering angle needed to ride safely?
This is complicated, because bikes steer by turning the fork and by leaning. At very low speeds, we steer mostly by turning, not leaning.

Wikipedia gives the formula for figuring this out, although you need to transpose some terms, you need to know the bike's dimensions, and you need to decide the radius of your turn.

Based on that formula, and assuming a bike with a head angle of 72°, a wheelbase of 1000 mm, and a desired turning radius of 5 meters, you get about 37°. A longer wheelbase will increase that angle slightly; a steeper head angle will increase that angle more; a tighter turning radius will increase it yet again.