Dont think there are gaskets, I havnt pulled mine off yet but I have not heard of them, nor have I seen them for sale. And if there anything like the catback hook up its just 2 pipes, ones flanged out so the other fits onto it.
Yep there is a gasket on one side. The side with the rectangle end on it. Most of the time the gasket is ok, but you can get it at most parts stores and ford will probably have it in stock. Which mid pipe did you get? I didn't need extensions with mine. You just unclip the 02 sensor wiring harness's from there retainers under the hood and it will give you alot more slack. I am assuming you are not buying a tuner? If not then yes you need elimantors, if you are then you just turn em off with the tuner.