Silver Plate Items: I do recommend hand washing items and hand drying them. This helps reduce tarnishing (as a lot of dishwashing detergents contain bleach) as well as water spots. As vintage silver plated items naturally tarnish over time, just use a polishing cloth to remove tarnish.
Pennies: Depending on the humidity where you live, pennies may tarnish quicker once they have been stamped. Using a polishing cloth can quickly remove the tarnish while still leaving the ink in the stamped portion.
Coffee Mugs: All my mugs are microwave and dishwasher safe.