ADDRESSES: You can choose to address your invitations by hand, or you can decide to print labels. Don't let the WIC bully you into thinking your own handwriting isn't good enough, or that the convenience of labels is tacky. As for the actual addresses, here are a few tips on how to address invitations formally, accounting for a whole host of last name conventions.
POSTAGE and Quantities: The number one tip you need when it comes to sending out your invites, is that your guest list number does not equal the number of invites your sending. Do the math on how many couples you have ahead of time, and you won't make the common mistake of ordering about double the invites you need.