I would use alcohol wipes for the surface. I would then take out the battery and use a combination of pipe cleaners and toothpicks along with rubbing alcohol to clean the crevices.

As always be careful. You could void your warranty with liquids or insertions.

This question really can vary depending on what type of business you operate. I know for me, that we use targeted approach because our clients and customers are not the typical day to day customers normal businesses would target.

If your client/customer base varies through the entire population spectrum it might be best to go city wide. However, if your money is generated from specific type of clientele I would reassess what value that might bring to the business that city wide may not.