A: GALFIT can always fit something, but not all fits are physically meaningful, and what's meaningful or not is often open to interpretation. Many different kinds of non-axisymmetric galaxies can be fit well, especially using new features or using multiple components. The current real limitations are perturbations in spiral arms, or spiral winding that is not logarithmic or hyperbolic-tangent in radius, e.g. a spiral arm that wind back onto itself. Despite these limitations, most of the time GALFIT will allow one to do much more than the actual science requires.
This falls under the technical FAQ section, which is located here.
This again falls under the technical FAQ section, which is located here.