Shelf life for oil, any motor oil for that matter including gear oil is about 5 years. That is oil in sealed container and not exposed to atmosphere or extreme changes in temperatures. Spark plugs exposed to air will oxidized and can even develop verdigris if not in used. Although you can probably clean them up and re-used them, you're probably better off just replacing them to have a clean slate as they don't cost that much. Compare if you have to spend time troubleshooting because you have improperly working plugs. No special oil needed to spray into the cylinders just simple 50:1 fuel mix, the same one you will use for the fuel tank. And yes, you can spray carb cleaner on the carbs.