Packaging And Embellishments: If you're adding embellishments, or you're mailing more than just an invite plus an RSVP card (we opted to mail more info, because of the destination aspect), keep track of the weight of your invitation suite once it's all packed up. Depending on its size, you may be facing more postage fees than a simple stamp will cover. You can get a postage estimate using a kitchen scale and checking on the USPS website. Through the USPS website I also learned that square invites and envelopes cost more in postage, by a significant amount. It's not worth it.
ONLINE PRINTING: There's a pretty wide variety when it comes printing via online companies, so always make sure you can get a proof of your invitation. With some companies, that may cost extra, but it's usually not very much. Much like with at_home printing, your paper options will usually be limited to whatever the company carries, and each company's paper set is going to be slightly different. You can usually request paper samples for free. Here are a few companies I've used with good results: