Coating rusting metal roofs

We purchased some light industrial buildings in Houston that were built in the 1970s and 1980s. There is rusting but its not that bad and it barely leaks. Should we be doing some preventative maintenance to stop future rust or wait to do a complete recoating. If we do recoat, do you have any suggestions? Some roofers have suggested replacing all of the screws that are backing out, but like I said before we rarely have leaks. Keep in mind that we have over 200,000 SF of roof. Thanks for the advice.

To do it right? Or what is your objective? I’ll throw a ladder and spit on it for $50.00