Great list! I'd like to add something:
If you are shipping a valuable item (any amount you are afraid to lose), don't buy your USPS postage online through paypal. Instead, take it to the post office and ship it from there. The reason? When you buy your postage through paypal and drop the item off at the post office, they DON'T SCAN IT upon departure. You get that "The seller informed USPS that they were shipping on this date" message when you track online until the item is either scanned along the way or when it is delivered. The problem is, if it isn't scanned when you send it out you have no proof it was ever sent if later it is lost! At least if you take it to the post office in person they scan the sig confirmation form and insurance before they ship it, so it will show up as sent!