We intend to install steam tracing on a pump for the purposes of maintaining a certain temperature, which enables the fluid in the pump to remain in liquid form.

What are the considerations for doing the heat transfer calculations for the required steam tracing?

The factors you mention have little or nothing to do with effectively maintaining the pump casing hot when you consider the practical aspects of what you are proposing.  The amount of liquid in the casing is static so you have an unsteady state heat transfer case.  The time that it takes to heat the liquid may not be important as just keeping it hot.  The remaining other factors (casing face surface area, heat transfer coefficients) should also be of little concern for what you are trying to do.  You are probably looking at a surface area of approximately 1.0 ft² or less.   Besides, you haven