I use medium consistency buttercream with a very large star tip. Start at the outside edge and work in a circle. Continue until you get to the center, release pressure and pull up! Happy baking! Missey
Yes, it candy melts. I added shortening to the candy melts to make it more pourable. Just drop your Oreo in to the bowl of melted candy, remove using a fork and lay on a cooling rack. They dry pretty quickly.
It's a visual thing. Some candy melts are more smooth than others. I would start at adding 1/4 teaspoon and add more as needed. White and brown candy melts seem to not need as much if any at all. Blue seems to need a lot. Just add enough that you can easily dip the Oreos and get nice results.
No, I've never added extra flavor. I like the Oreo flavor to stand out. but I bet mint flavor would be nice with the chocolate and cream flavor.
BTW, I've heard a great mock Girl Scout Mint cookie is to take a Ritz cracker and cover it in mint flavored chocolate. I don't like mint, so I've never tried it. but I've heard of several decorators that have done this and swear by it.
You can cover absolutely anything you want. Candy melts are a great way to start until you learn how to properly temper chocolate.