Not a fan of WD40 for running parts. Usually use light citrus for chain, jockey wheels and the like. Rinse off with hot water and let dry. Reassemble & lube. Light spray of citrus, WD or even Windex on a soft cloth for wiping down everything else…but I’m not usually in a hurry and I don’t have customers queuing for their bikes.
YES! Thank god!!! This crazy man tech also works on thing like cars, boats and even small humans.
Fun fact: WD40 was developed as a Lube and rust preventor during one of those big wars ages ago for the barrels of big ass cannons mounted near the sea as the salty air would yadda, yadda, you get it. It also make a great Father’s Day present 
No, not really. Not rocket science hey, just try and see what suits the job.