Regarding scheduling...we use something called PBS, which stands for Pilots Butts in Seats. This unique system insures the trips are properly staffed and deconflicts known absences and training and other conflicts and puts pilots booties in the seat. Seniority is used, but the reality is it depends on overall solution constraints. this is where the black magic and unicorns comes in. Your preferences are racked and stacked against other pilots preferences, and the procedure is somewhat reminiscent of the lottery system.
Also utilized is the G line. Not to be confused with the G string, or the G spot, the G line is the published line you want to be above in order to guarantee you won't be on reserve. However, the G line floats from month to month and it's in flux much like how the magnetic north pole floats about.