Good advice so far. With a Shield 9mm and decent ammo I would not over achieve on cleaning. After 150-200 rounds, a field strip and good wipe down of all components and bore snake of simple cleaning of the bore. Assemble and a light we with your lube of choice.
After 500 or so, field strip and a detailed cleaning, making sure the extractor is clear of gunk and frame parts as well. Consider a brush and solvent down the bore and patches until they come out clean. Lube per manual, though intend to use a quality grease at wear points, YMMV.
I have a number of Shield magazines, so none are really showing any wear. The only metal magazines I've replaced due to wear were 1911 ones and that was due to the magazine lips spreading, vice the springs. If you get failures to feed after extend use, consider the springs. I don't know what the "no go" specs would be for a Shield magazine feed lips. Maybe someone else does.
Overall anti-corrosion for the external surfaces depends on your climate, how much you carry and how (IWB, OWB etc) and the lube/protectant you use.
Enjoy your Shield