Before or after you load, doesn't matter. Tires deform; they don't compress, so the air pressure remains the same regardless of how much weight you put on them.
Max PSI is "safe" but not necessarily necessary. Without knowing what tires you have or how much weight you plan to put on them, this is what I would recommend, though. You will sacrifice some wear on the tires by doing it this way, but again, it is the "safe" way to go.