How do I determine the courtyard for a component footprint?
The best answer is probably to follow IPC-7351 3.1.5.4. There are some tables that give guidelines as to the excess to leave around a component or pad, whichever is bigger- maybe 0.1 to 0.5mm in most (not all) cases.
The standard specifically states that the courtyard is the starting point for the minimum area for the component, and there may be a manufacturing allowance that is dependent on factors that are not part of the standard.
I've linked the working draft standard (2008) above, direct from the ipc.org website. The actual standard costs money so any copies you might find floating around probably represent copyright infringement.